The function to get DHCP Inventory along with reservations. It uses PS jobs so even if you have many DHCP servers in org or many scopes, it should be done within mins

Get-DHCPInventory.ps1

$logpath = "c:\temp\logfile.txt"

function Write-Log {
    [CmdletBinding()]
    Param(
        [Parameter(ValueFromPipeline = $true, mandatory = $true)]$logtext,
        [Parameter(ValueFromPipeline = $true, mandatory = $true)]$logpath
    )

    $Stamp = (Get-Date).toString("yyyy/MM/dd HH:mm:ss")
    $LogMessage = "$Stamp : $logtext"
    
    $isWritten = $false

    do {
        try {
            Add-content $logpath -value $LogMessage -Force -ErrorAction SilentlyContinue
            $isWritten = $true
        }
        catch {
        }
    } until ( $isWritten )
}

function New-BaloonNotification {
    Param(
        [Parameter(ValueFromPipeline = $true, mandatory = $true)][String]$title,
        [Parameter(ValueFromPipeline = $true, mandatory = $true)][String]$message,        
        [Parameter(ValueFromPipeline = $true, mandatory = $false)][ValidateSet('None', 'Info', 'Warning', 'Error')][String]$icon = "Info",
        [Parameter(ValueFromPipeline = $true, mandatory = $false)][scriptblock]$Script
    )
    Add-Type -AssemblyName System.Windows.Forms

    if ($null -eq $script:balloonToolTip) { $script:balloonToolTip = New-Object System.Windows.Forms.NotifyIcon }

    $tip = New-Object System.Windows.Forms.NotifyIcon

    $path = Get-Process -id $pid | Select-Object -ExpandProperty Path
    $tip.Icon = [System.Drawing.Icon]::ExtractAssociatedIcon($path)
    $tip.BalloonTipIcon = $Icon
    $tip.BalloonTipText = $message
    $tip.BalloonTipTitle = $title    
    $tip.Visible = $true            
    
    try {
        register-objectevent $tip BalloonTipClicked BalloonClicked_event -Action { $script.Invoke() } | Out-Null
    }
    catch {}
    $tip.ShowBalloonTip(10000) # Even if we set it for 1000 milliseconds, it usually follows OS minimum 10 seconds
    Start-Sleep -seconds 1
    
    $tip.Dispose() # Important to dispose otherwise the icon stays in notifications till reboot
    Get-EventSubscriber -SourceIdentifier "BalloonClicked_event"  -ErrorAction SilentlyContinue | Unregister-Event # In case if the Event Subscription is not disposed
}

Function Get-DHCPInventory {
    # Variable declaration
    
    $jobs = @()
    $maxParallelJobs = 50

    # Get all Authorized DCs from AD configuration
    $DHCPs = Get-DhcpServerInDC

    $scriptBlock1 = ${function:Write-log}
    $scriptBlock2 = ${function:New-BaloonNotification}
    
    $initScript = [scriptblock]::Create(@"
    function Write-log {$scriptBlock1}
    function New-BaloonNotification {$scriptBlock2}
"@)

    foreach ($dhcp in $DHCPs) {
        while ((Get-Job -State Running).Count -ge $maxParallelJobs) {
            Start-Sleep -Milliseconds 50  # Wait for 0.05 seconds before checking again
        }        

        $ScriptBlock = {
            param($dhcp, $logpath)

            $Report = @()
            $Reservations = @()
            $Summary = @()

            if ((Test-Connection -ComputerName $dhcp.DNSName -count 2 -Quiet ) -AND (Get-Service -Name DHCPServer -ComputerName $dhcp.DNSName -ErrorAction SilentlyContinue).Status -eq "Running") {                 
                $scopes = $null
                $scopes = (Get-DhcpServerv4Scope -ComputerName $dhcp.DNSName -ErrorAction SilentlyContinue)
                
                try {
                    $OS = (Get-WmiObject win32_operatingSystem -ComputerName $dhcp.DNSName -Property Caption -ErrorAction SilentlyContinue).Caption                
                }
                catch {
                    $OS = "Access denied"                        
                    Write-Log -logtext "Could not get operating system details for DHCP Server $($dhcp.DNSName) : $($_.Exception.Message)" -logpath $logpath
                }                    

                If ($scopes) {
                    try {
                        $GlobalOptions = Get-DhcpServerv4OptionValue -OptionId 6, 15 -ComputerName $dhcp.DNSName -ErrorAction SilentlyContinue                        
                        $Option015 = [string]($Globaloptions | Where-Object { $_.optionID -eq 15 } ).Value
                        $GlobalDNSList = ($Globaloptions | Where-Object { $_.optionID -eq 6 } ).Value
                        
                        if ($GlobalDNSList) {
                            $GlobalDNS1 = $GlobalDNSList[0]
                            $GlobalDNS2 = $GlobalDNSList[1]
                            $GlobalDNS3 = $GlobalDNSList[2]
                        }
                    }
                    catch {
                        Write-Log -logtext "Could not get option values (6 or 15) from DHCP Server $($dhcp.DNSName) : $($_.Exception.Message)" -logpath $logpath                        
                    }

                    $NoLeaseScopes = @()
                    foreach ($Scope in $scopes) {
                        $Leases = Get-DhcpServerv4Lease -ComputerName $dhcp.DNSName -ScopeId $Scope.ScopeId -ErrorAction SilentlyContinue
                        if ($Leases.Count -eq 0) {
                            $NoLeaseScopes += $Scope.ScopeID
                        }
                    }

                    $scopes | ForEach-Object {
                        try {
                            $ScopeOptions = Get-DhcpServerv4OptionValue -OptionId 3, 6, 15, 160, 234 -ScopeID $_.ScopeId -ComputerName $dhcp.DNSName -ErrorAction SilentlyContinue
                            
                            $gateways = ($ScopeOptions | Where-Object { $_.optionID -eq 3 } ).Value
                            if ($gateways) {
                                $gateway = $gateways[0]
                            }
                            
                            $ScopeOption015 = [string]($ScopeOptions | Where-Object { $_.optionID -eq 15 } ).Value
                            $ScopeOption160 = [string]($ScopeOptions | Where-Object { $_.optionID -eq 160 } ).Value
                            $DoGroupId = [string]($ScopeOptions | Where-Object { $_.optionID -eq 234 } ).Value
                            $ScopeDNSList = ($ScopeOptions | Where-Object { $_.optionID -eq 6 } ).Value

                            if ($ScopeDNSList) {
                                $ScopeDNS1 = $ScopeDNSList[0]
                                $ScopeDNS2 = $ScopeDNSList[1]
                                $ScopeDNS3 = $ScopeDNSList[2]
                            }
                        }
                        catch {
                            Write-Log -logtext "Could not get option values (3,15,160,234) for Scope $($_.Name) on DHCP Server $($dhcp.DNSName) : $($_.Exception.Message)" -logpath $logpath
                        }
                        
                        Try { 
                            $ScopeExclusions = Get-DhcpServerv4ExclusionRange -ComputerName $dhcp.DNSName -ScopeID $_.ScopeId -ErrorAction SilentlyContinue | Select-Object @{l = "Exclusions"; e = { "$($_.StartRange.IPAddressToString) - $($_.EndRange.IPAddressToString)" } }
                        }
                        Catch { 
                            Write-Log -logtext "Issue in getting exclusio details for scope $($_.Name) from DHCP Server $($dhcp.DNSName) : $($_.Exception.Message)" -logpath $logpath
                        }

                        try {
                            $ResValues = Get-DhcpServerv4Reservation -ComputerName $dhcp.DNSName -ScopeID $_.ScopeID -ErrorAction SilentlyContinue | Select-Object ScopeId, IPAddress, Name, Description, ClientID, AddressState
                            $ResValues | ForEach-Object {
                                $Reservation = [PSCustomObject]@{
                                    ServerName   = $dhcp.DNSName
                                    ScopeID      = $_.ScopeId
                                    IPAddress    = $_.IPAddress
                                    HostName     = $_.Name
                                    Description  = $_.Description
                                    ClientID     = $_.ClientID
                                    AddressState = $_.AddressState
                                }

                                $Reservations += $Reservation
                            }
                        }
                        catch {
                            Write-Log -logtext "Could not get reservation details for scope $($_.ScopeID) on DHCP Server $($dhcp.DNSName) : $($_.Exception.Message)" -logpath $logpath        
                        }                        

                        $ScopeDetail = [PSCustomObject]@{
                            DHCPName       = $dhcp.DNSName
                            DHCPAddress    = $dhcp.IPAddress
                            ScopeID        = $_.ScopeID
                            SubnetMask     = $_.SubnetMask
                            Gateway        = $gateway
                            ScopeName      = $_.Name
                            State          = $_.State
                            StartRange     = $_.StartRange
                            Endrange       = $_.EndRange
                            LeaseDuration  = $_.LeaseDuration
                            Description    = $_.Description
                            ScopeOption15  = $ScopeOption015
                            Exclusions     = $ScopeExclusions.Exclusions -join "`n"
                            GlobalOption15 = $Option015
                            DOGroupID      = $DoGroupID
                            Option160      = $ScopeOption160
                            ScopeDNS1      = $ScopeDNS1
                            ScopeDNS2      = $ScopeDNS2
                            ScopeDNS3      = $ScopeDNS3
                            GlobalDNS1     = $GlobalDNS1
                            GlobalDNS2     = $GlobalDNS2
                            GlobalDNS3     = $GlobalDNS3                            
                        }

                        $Report += $ScopeDetail
                    }

                    $Summary += [PSCustomObject]@{
                        DHCPName           = $dhcp.DNSName
                        DHCPAddress        = $dhcp.IPAddress
                        OperatingSystem    = $OS
                        ScopeCount         = $scopes.count
                        InactiveScopeCount = @($scopes | Where-Object { $_.State -eq 'Inactive' }).count
                        ScopeWithNoLease   = $NoLeaseScopes -join "`n"
                        NoLeaseScopeCount  = $NoLeaseScopes.count
                    }
                }
                else {
                    $message = "No scopes found on the DHCP Server $($dhcp.DNSName)."
                    New-BaloonNotification -title "Information" -message $message
                    Write-Log -logtext $message -logpath $logpath

                    $Summary += [PSCustomObject]@{
                        DHCPName           = $dhcp.DNSName
                        DHCPAddress        = $dhcp.IPAddress
                        OperatingSystem    = $OS
                        ScopeCount         = 0
                        InactiveScopeCount = 0
                        ScopeWithNoLease   = ""
                        NoLeaseScopeCount  = 0
                    }

                    $ScopeDetail = [PSCustomObject]@{
                        DHCPName       = $dhcp.DNSName
                        DHCPAddress    = $dhcp.IPAddress
                        ScopeID        = "No scopes"
                        SubnetMask     = "No scopes"
                        Gateway        = "No scopes"
                        ScopeName      = "No scopes"
                        State          = "No scopes"
                        StartRange     = "No scopes"
                        Endrange       = "No scopes"
                        LeaseDuration  = "No scopes"
                        Description    = "No scopes"
                        ScopeDNS1      = "No scopes"
                        ScopeDNS2      = "No scopes"
                        ScopeDNS3      = "No scopes"
                        ScopeOption15  = "No scopes"
                        Exclusions     = "No scopes"
                        GlobalDNS1     = "No scopes"
                        GlobalDNS2     = "No scopes"
                        GlobalDNS3     = "No scopes"
                        GlobalOption15 = "No scopes"
                        DOGroupID      = "No scopes"
                        Option160      = "No scopes"
                    }

                    $Report += $ScopeDetail
                }                
            }
            else {
                $message = "The DHCP Server $($dhcp.DNSName) not reachable or the service is stopped, would be skipped."
                New-BaloonNotification -title "Information" -message $message
                Write-Log -logtext $message -logpath $logpath

                $Summary += [PSCustomObject]@{
                    DHCPName           = $dhcp.DNSName
                    DHCPAddress        = $dhcp.IPAddress
                    OperatingSystem    = ""
                    ScopeCount         = 0
                    InactiveScopeCount = 0
                    ScopeWithNoLease   = ""
                    NoLeaseScopeCount  = 0
                }

                $ScopeDetail = [PSCustomObject]@{
                    DHCPName       = $dhcp.DNSName
                    DHCPAddress    = $dhcp.IPAddress
                    ScopeID        = "Not reachable"
                    SubnetMask     = "Not reachable"
                    Gateway        = "Not reachable"
                    ScopeName      = "Not reachable"
                    State          = "Not reachable"
                    StartRange     = "Not reachable"
                    Endrange       = "Not reachable"
                    LeaseDuration  = "Not reachable"
                    Description    = "Not reachable"
                    ScopeDNS1      = "Not reachable"
                    ScopeDNS2      = "Not reachable"
                    ScopeDNS3      = "Not reachable"
                    ScopeOption15  = "Not reachable"
                    Exclusions     = "Not reachable"
                    GlobalDNS1     = "Not reachable"
                    GlobalDNS2     = "Not reachable"
                    GlobalDNS3     = "Not reachable"
                    GlobalOption15 = "Not reachable"
                    DOGroupID      = "Not reachable"
                    Option160      = "Not reachable"
                }

                $Report += $ScopeDetail | Select-Object DHCPName, DHCPAddress, ScopeName, Description, ScopeID, SubnetMask, StartRange, Endrange, LeaseDuration, State, Gateway, ScopeOption15, Exclusions, DOGroupID, Option160, GlobalOption15, ScopeDNS1, ScopeDNS2, ScopeDNS3, GlobalDNS1, GlobalDNS2, GlobalDNS3
            }

            $message = "Working over DHCP Server $($dhcp.DNSName) related details."
            New-BaloonNotification -title "Information" -message $message
            Write-Log -logtext $message -logpath $logpath

            $Output = [PSCustomObject]@{
                Report      = $Report
                Reservation = $Reservations
                Summary     = $Summary
            }

            return $Output
        }

        $jobs += Start-Job -ScriptBlock $scriptBlock -ArgumentList $dhcp, $logpath -InitializationScript $initscript
    }

    Write-Log -logtext "Powershell jobs submitted for looking into $($DHCPs.count) DHCP Server details" -logpath $logpath
    $null = $jobs | Wait-Job 

    $result = @()
    foreach ($job in $jobs) {
        $result += Receive-Job -Job $job
    }
    $null = Get-Job | remove-Job

    Write-Log -logtext "Powershell jobs completed for $($DHCPs.count) DHCP Server details" -logpath $logpath
    
    $Details = [pscustomobject] @{
        Inventory   = $result.Report
        Reservation = $result.Reservation
        Summary     = $result.Summary
    }
    
    Return $Details
}

$s = Get-DHCPInventory
$s.Summary | Format-Table *
$s.Inventory | Format-Table *
$s.Reservation | Format-Table *