Sample that will disable the guest sharing option on all SPO sites that currently have no external external users on them.

Disable-ExternalSharingOnSitesWithNoGuestAccounts.ps1

[System.Net.WebRequest]::DefaultWebProxy.Credentials = [System.Net.CredentialCache]::DefaultCredentials 
[System.Net.ServicePointManager]::SecurityProtocol = [System.Net.SecurityProtocolType]::Tls11 -bor [System.Net.SecurityProtocolType]::Tls12   

# start logging
$transcriptFile = if([string]::IsNullOrWhiteSpace($MyInvocation.MyCommand.Name)) { "Set-TeamsChannelStorageQuota.ps1" }else{ $MyInvocation.MyCommand.Name }
$transcriptPath = "$($transcriptFile)_$(Get-Date -Format FileDateTime).log"
Start-Transcript -Path $transcriptPath

# clear error history
$Error.Clear() 

# load module
Import-Module -Name SharePointPnPPowerShellOnline -WarningAction SilentlyContinue

function Set-TeamsChannelStorageQuota
{
    [CmdletBinding()]
    param
    (
        [Parameter(Mandatory=$true,ValueFromPipeline=$true)][Microsoft.Online.SharePoint.TenantAdministration.SiteProperties]$SiteProperties,
        [Parameter(Mandatory=$false)][int]$StorageMaximumLevel = (1GB/1MB)   <# 1GB   #>,
        [Parameter(Mandatory=$false)][int]$StorageWarningLevel = (500MB/1MB) <# 500MB #>,
        [Parameter(Mandatory=$false)][switch]$RetainCurrentStorageMaximumLevelIfHigher,
        [Parameter(Mandatory=$false)][switch]$WhatIf
    )
    
    begin
    {
    }
    process
    {
        $NewStorageMaximumLevel = $StorageMaximumLevel
        $NewStorageWarningLevel = $StorageWarningLevel

        Write-Verbose -Message "$($SiteProperties.Url) - StorageMaximumLevel: $($SiteProperties.StorageMaximumLevel)"
        Write-Verbose -Message "$($SiteProperties.Url) - StorageWarningLevel: $($SiteProperties.StorageWarningLevel)"

        if( $SiteProperties.StorageMaximumLevel -eq (25TB/1MB) )
        {
            # channel has default 25TB quota, change it to default or supplied value
        }
        elseif( $RetainCurrentStorageMaximumLevelIfHigher.IsPresent )
        {
            $NewStorageMaximumLevel = [System.Math]::Max( $StorageMaximumLevel, $SiteProperties.StorageMaximumLevel )
            $NewStorageWarningLevel = [System.Math]::Max( $StorageWarningLevel, $SiteProperties.StorageWarningLevel )
        }

        if( $WhatIf.IsPresent )
        {
            if( $SiteProperties.StorageMaximumLevel -ne $NewStorageMaximumLevel -and $SiteProperties.StorageWarningLevel -ne $NewStorageWarningLevel)
            {
                Write-Output "$($SiteProperties.Url) - Would have changed StorageMaximumLevel from $($SiteProperties.StorageMaximumLevel) to $NewStorageMaximumLevel and StorageWarningLevel from $($SiteProperties.StorageWarningLevel) to $NewStorageWarningLevel"
            }
            else
            {
                Write-Output "$($SiteProperties.Url) - No changes required"
            }
        }
        else
        {
            if( $SiteProperties.StorageMaximumLevel -ne $NewStorageMaximumLevel-and $SiteProperties.StorageWarningLevel -ne $NewStorageWarningLevel)
            {
                Write-Verbose -Message "$($SiteProperties.Url) - Changing StorageMaximumLevel from $($SiteProperties.StorageMaximumLevel) to $NewStorageMaximumLevel and StorageWarningLevel from $($SiteProperties.StorageWarningLevel) to $NewStorageWarningLevel"
                Set-PnPTenantSite -Url $SiteProperties.Url -StorageMaximumLevel $NewStorageMaximumLevel -StorageWarningLevel $NewStorageWarningLevel
            }
        }
    }
    end
    {
    }
}

function Send-ExecutionSummary
{
    [CmdletBinding()]
    param
    (
        [Parameter(Mandatory=$true)][string]$SmtpServer,
        [Parameter(Mandatory=$true)][string[]]$To,
        [Parameter(Mandatory=$true)][string]$From,
        [Parameter(Mandatory=$false)][string[]]$Cc,
        [Parameter(Mandatory=$true)][string]$TranscriptPath
    )
    
    begin
    {
        $head = "
            <style>
                h1 {
                    font-family: Arial, Helvetica, sans-serif;
                    color: #e68a00;
                    font-size: 28px;
                }
                h2 {
                    font-family: Arial, Helvetica, sans-serif;
                    color: #000099;
                    font-size: 16px;
                }
                table {
		            font-size: 12px;
		            border: 0px; 
		            font-family: Arial, Helvetica, sans-serif;
	            } 
                td {
		            padding: 4px;
		            margin: 0px;
		            border: 0;
	            }
                th {
                    background: #395870;
                    background: linear-gradient(#49708f, #293f50);
                    color: #fff;
                    font-size: 11px;
                    text-transform: uppercase;
                    padding: 10px 15px;
                    vertical-align: middle;
	            }

                tbody tr:nth-child(even) {
                    background: #f0f0f2;
                }
            </style>"

        if( $Error.Count -eq 0 )
        {
            $result = "SUCCESS"
        }
        else
        {
            $result = "FAILURE"
        }
        
        $errors = ""

        $body = [PSCustomObject] @{
                    Computer   = $env:COMPUTERNAME
                    Script     = $MyInvocation.MyCommand.Name
                    Result     = $result
                    Transcript = $TranscriptPath
                } | ConvertTo-Html -PreContent "<h2>Execution Summary</h2>" -As Table

        $params = @{
            SmtpServer = $SmtpServer
            To         = $To
            From       = $From
            Cc         = $Cc
            Subject    = "$($env:COMPUTERNAME) - $($MyInvocation.MyCommand.Name) - $result"
            Body       = $body
            BodyAsHtml = $true
            Priority   = "Normal"
        }
    }
    process
    {
        if( $Error.Count -gt 0 )
        {
            $errors = ($Error | ConvertTo-Html -As Table -Fragment -PreContent "<h2>Summary of $($Error.Count) Exceptions</h2>") -join "`n"
        }

        $params["Body"] = ConvertTo-Html -Body "$body $errors" -Head $head -As List
        #$params["Body"] | Set-Content -Path "C:\_temp\debug.html" 

        Send-MailMessage @params
    }
    end
    {
    }    
}

# requires Azure AD App Principals > SharePoint > Sites.FullControl.All permissions 
$tenant              = "contoso"
$clientId            = "8a6b10a8-1234-1234-1234-9b8e49b6f6b7"
$certificatePath     = "E:\_certs\AppPrincipalCert.pfx"
$certificatePassword = ConvertTo-SecureString -String 'pass@word1' -AsPlainText -Force

# connect to the tenant
Connect-PnPOnline -Url "https://$tenant-admin.sharepoint.com" -ClientId $clientId -CertificatePath $certificatePath -CertificatePassword $certificatePassword -Tenant "$tenant.onmicrosoft.com" -WarningAction SilentlyContinue

# get all channels with StorageMaximumLevel > 1GB
$channels = Get-PnPTenantSite -Template "TEAMCHANNEL#0" | ? StorageMaximumLevel -gt 1GB

# process each channel
$channels | Set-TeamsChannelStorageQuota -Verbose -RetainCurrentStorageMaximumLevelIfHigher -WhatIf

# send email summary
Send-ExecutionSummary -SmtpServer "mail.contoso.com" -To "joe.smith@contoso.com" -From "automation@contoso.com" -TranscriptPath $transcriptPath

# stop logging
Stop-Transcript