The following Sitecore PowerShell Extensions script finds items stored in the IAR files that also exist in the database.

Delete.ps1

$databaseName = $actionData["databaseName"]
$filename = $actionData["filename"]

$resourceLoaderType = ([System.Type]::GetType("Sitecore.Data.DataProviders.ReadOnly.Protobuf.IResourceLoader, Sitecore.Data.ResourceItems.ProtobufNet"))
$resourceLoader = [Sitecore.DependencyInjection.ServiceLocator]::ServiceProvider.GetService($resourceLoaderType)
$paths = [System.Collections.Generic.List[String]]@()
$paths.Add([Sitecore.MainUtil]::MapPath("/App_Data/items/$($databaseName)/$($filename)")) > $null
$paths.Add([Sitecore.MainUtil]::MapPath("/sitecore modules/items/$($databaseName)/$($filename)")) > $null
$defaultFieldValues = New-Object -TypeName 'System.Collections.Generic.Dictionary[[guid], [string]]'
$database = [Sitecore.Configuration.Factory]::GetDatabase($databaseName)
$connectionString = [System.Configuration.ConfigurationManager]::ConnectionStrings[$databaseName]
$callContext = New-Object -TypeName "Sitecore.Data.DataProviders.CallContext, Sitecore.Kernel" -ArgumentList @($database.DataManager, $database.DataProviders.Count)
$sqlDataProvider = New-Object -TypeName "Sitecore.Data.SqlServer.SqlServerDataProvider, Sitecore.Kernel" -ArgumentList @($connectionString)

foreach($item in $selectedData) {
    $itemDefinition = $sqlDataProvider.GetItemDefinition($item.ID, $callContext)
    if($itemDefinition) {
        $sqlDataProvider.DeleteItem($itemDefinition, $callContext) > $null
    }
}

$reportItems = [System.Collections.ArrayList]@()
$itemDataSet = $resourceLoader.LoadFromFiles($paths, "dat", $defaultFieldValues)
foreach($itemRecord in $itemDataSet.Definitions.Values) {
    $id = New-Object -TypeName "Sitecore.Data.ID, Sitecore.Kernel" -ArgumentList @($itemRecord.ID)
    $itemDefinition = $sqlDataProvider.GetItemDefinition($id, $callContext)
    if($itemDefinition) {
        $reportItems.Add((Get-Item -Path "$($databaseName):" -ID ([ID]::Parse($itemRecord.ID)))) > $null
    }
}

$reportItems | Update-ListView

FilesMissingRevision.ps1

$folder = "C:\Work\company\app\src\Serialization"
$files = Get-ChildItem -Path $folder -Recurse -File -Filter "*.yml"
foreach($file in $files) {
    $content = [System.IO.File]::ReadAllText($file.FullName)
    if(!$content.Contains("__Revision") -and !$content.Contains("MemberOf:")) {
        Write-Host "$($file.FullName)"
        #Remove-Item -Path $file.FullName
    }
}

GetModifiedItems.ps1

#https://www.maartenwillebrands.nl/2022/02/15/sitecore-removing-iar-items-from-the-database/

function Get-ModifiedItem {
    param(
        $databaseName,
        $filename
    )
    
    $resourceLoaderType = ([System.Type]::GetType("Sitecore.Data.DataProviders.ReadOnly.Protobuf.IResourceLoader, Sitecore.Data.ResourceItems.ProtobufNet"))
    $resourceLoader = [Sitecore.DependencyInjection.ServiceLocator]::ServiceProvider.GetService($resourceLoaderType)
    $paths = [System.Collections.Generic.List[String]]@()
    $paths.Add([Sitecore.MainUtil]::MapPath("/App_Data/items/$($databaseName)/$($filename)")) > $null
    $paths.Add([Sitecore.MainUtil]::MapPath("/sitecore modules/items/$($databaseName)/$($filename)")) > $null
    $defaultFieldValues = New-Object -TypeName 'System.Collections.Generic.Dictionary[[guid], [string]]'

    $database = [Sitecore.Configuration.Factory]::GetDatabase($databaseName)
    $connectionString = [System.Configuration.ConfigurationManager]::ConnectionStrings[$databaseName]
    $callContext = New-Object -TypeName "Sitecore.Data.DataProviders.CallContext, Sitecore.Kernel" -ArgumentList @($database.DataManager, $database.DataProviders.Count)
    $sqlDataProvider = New-Object -TypeName "Sitecore.Data.SqlServer.SqlServerDataProvider, Sitecore.Kernel" -ArgumentList @($connectionString)

    $itemDataSet = $resourceLoader.LoadFromFiles($paths, "dat", $defaultFieldValues)
    foreach($itemRecord in $itemDataSet.Definitions.Values) {
        <# Find Items in database and IAR file
        $id = New-Object -TypeName "Sitecore.Data.ID, Sitecore.Kernel" -ArgumentList @($itemRecord.ID)
        $itemDefinition = $sqlDataProvider.GetItemDefinition($id, $callContext)
        if($itemDefinition) {
            Get-Item -Path "$($databaseName):" -ID ([ID]::Parse($itemRecord.ID))
        }
        #>
        <# Find items where a language version is missing
        $item = Get-Item -Path "$($databaseName):" -ID ([ID]::Parse($itemRecord.ID))
        if($item.Versions.GetVersions($true).Count -eq 0) {
            $item
            #Add-ItemVersion -Item $item -TargetLanguage "en" -IfExist Skip -IfNoSourceVersion Add
        } else {
            #$item
        }
        #>
        <# Update revision on items which use the Standard Value
        $id = New-Object -TypeName "Sitecore.Data.ID, Sitecore.Kernel" -ArgumentList @($itemRecord.ID)
        $itemDefinition = $sqlDataProvider.GetItemDefinition($id, $callContext)
        if(!$itemDefinition) {
            $item = Get-Item -Path "$($databaseName):" -ID ([ID]::Parse($itemRecord.ID))
            if($item.Fields["__Revision"].ContainsStandardValue) {
                Write-Host "Saving revision for $($item.Paths.Path)"
                $item.Editing.BeginEdit()
                $item["__Updated by"] = "sitecore\admin"
                $item.Editing.EndEdit($true, $false) > $null
                $item
            }
        }
        #>
    }
}

$iarItemNames = Get-ChildItem -Path "$($AppPath)/sitecore modules/items/" -File -Filter *.dat -Recurse | Select-Object -ExpandProperty Name | Sort-Object

$options = [ordered]@{}
foreach($iarItemName in $iarItemNames) {
    $options[$iarItemName] = $iarItemName
}

$props = @{
    Parameters = @(
        @{Name="filename"; Title="Choose an option"; Tooltip="Additional details about the option"; Options=$options; }
    )
    Title = "Option Selector"
    Icon = "OfficeWhite/32x32/question.png"
    Description = "Choose an option."
    Width = 450
    Height = 300
    ShowHints = $true
}

$result = Read-Variable @props
if($result -eq "cancel"){
    exit
}

$databaseName = $filename.Split(".")[1]
Get-ModifiedItem -Database $databaseName -Filename $filename | Show-ListView -ViewName IARCleanup -ActionData @{"databaseName"=$databaseName;"filename"=$filename} -Property ID, Name, ItemPath, TemplateName, Database, Language, Version, @{Label="Revision";Expression={$_.__Revision}}

SaveWithRevision.ps1

$rootIds = @(
    "{B237CC51-F696-4D47-8467-BC988DF97686}",
    "{B44226A7-42CE-4192-ABC1-2248B47EF213}",
    "{0944417E-9A0D-4E65-B440-047E08BBA911}",
    "{015B07EF-AB67-44B7-A625-4F447ABF7BD2}",
    "{926401BF-A4E0-42A2-87B8-EBA8FF4FB5CF}",
    "{2F8232B5-3089-4FEB-999A-D7389C903BB2}",
    "{893839B9-14D9-4DA4-B504-51DC9E394DCF}",
    "{6332795D-398F-49D6-ABB6-B28972B87E3E}",
    "{8A071F63-95C6-46FC-AB37-926C7E1A46EA}",
    "{B0AACC00-9D03-4A7A-BF30-CCCCCB30A419}",
    "{A8615D05-BD21-4859-9340-892FBAEC64AB}",
    "{2FD6E0B8-7A41-4372-8F84-A9B2F5F7F009}",
    "{3ABF909C-980B-4A8B-BDE3-97048A1B18D4}",
    "{A7F3264E-39CA-4962-805B-AE3D97A3AD63}",
    "{1CE18C4B-1B27-469B-940B-45A2D9692178}",
    "{DD0F4430-91AA-455B-B792-1C0EB80B8763}",
    "{DF7836DE-0EA6-45E6-9530-402C7232A936}"
)


foreach($rootId in $rootIds) {
    Get-ChildItem -Path "master:" -ID $rootId -Recurse | ForEach-Object {
        $item = $_
        if($item.Fields["__Revision"].ContainsStandardValue -or [string]::IsNullOrEmpty($item.Fields["__Revision"])) {
            Write-Host "Saving revision for $($item.Paths.Path)"
            #$item.Editing.BeginEdit()
            #$item["__Updated by"] = "sitecore\admin"
            #$item.Editing.EndEdit($true, $false) > $null
        }
    }
}

StageRevisionChanges.ps1

$src = "C:\Work\company\"
Push-Location -Path $src
$files = git diff --name-only HEAD
foreach($file in $files) {
    Write-Host "Processing $($file)"
    $changes = git diff HEAD~1 $file
    $additions = 0
    $subtractions = 0
    foreach($line in $changes) {
        if($line.StartsWith("+ ")) {
            $additions++
        }
        if($line.StartsWith("- ")) {
            $subtractions++
        }
    }
    if($additions -eq 3 -and $subtractions -eq 0 -and $changes.Contains("+      Hint: __Revision")) {
        git add $file
    }
}
Pop-Location