Combine many Windows GPO backups into one. For working with live GPOs, consider this instead: https://learn.microsoft.com/en-us/archive/blogs/ashleymcglone/updated-copy-and-merge-group-policies-gpos-with-powershell

MergeGPOBackups.ps1

<#
    .SYNOPSIS
    Combines Group Policy Object (GPO) backups from multiple source directories
    into a single unified directory containing the GPO backups.

    .DESCRIPTION
    Combines Group Policy Object (GPO) backups from multiple source directories
    into a single unified directory containing the GPO backups.
    Duplicate GPOs will be ignored based on display name.

    .PARAMETER Sources
    Specifies the paths to the directories containing all the GPO backups to be
    merged.

    .PARAMETER Destination
    Specifies the path to the destination directory to contain all the GPO
    backups.
#>

#Requires -Version 7

[CmdletBinding()]
param (
    [Parameter(Mandatory)][string[]]$Sources,
    [Parameter(Mandatory)][string]$Destination
)

$manifestNamespace = @{mfst = 'http://www.microsoft.com/GroupPolicy/GPOOperations/Manifest' }

$finalManifest = [xml]'<Backups xmlns="http://www.microsoft.com/GroupPolicy/GPOOperations/Manifest"
xmlns:mfst="http://www.microsoft.com/GroupPolicy/GPOOperations/Manifest" mfst:version="1.0"></Backups>'

if (![System.IO.Directory]::Exists($Destination)) {
    Write-Verbose "Creating directory for merged GPO backups: $Destination"
    New-Item $Destination -ItemType Directory | Out-Null
}

foreach ($backupDir in Get-Item $Sources) {
    $manifestFile = [System.IO.Path]::Combine($backupDir, 'manifest.xml')

    if (![System.IO.File]::Exists($manifestFile)) {
        Write-Warning "Manifest file missing for GPO backup: $($backupDir.Name)"
        continue
    }

    Write-Verbose "Enumerating GPOs in backup: $($backupDir.Name)"

    Select-Xml -Path $manifestFile `
        -XPath '/mfst:Backups/mfst:BackupInst' `
        -Namespace $manifestNamespace `
    | ForEach-Object {

        $gpoDisplayName = $_.Node.GPODisplayName.InnerText
        $gpoId = $_.Node.ID.InnerText

        Write-Verbose "Found GPO: $gpoDisplayName"
        Write-Debug "ID is $gpoId"

        if (
            ($finalManifest | Select-Xml -XPath '/mfst:Backups/mfst:BackupInst/mfst:GPODisplayName' `
                -Namespace $manifestNamespace).Node.InnerText -contains $gpoDisplayName
        ) {
            Write-Verbose 'GPO is a duplicate; ignoring'
            continue
        }

        $gpoDir = [System.IO.Path]::Combine($backupDir, $gpoId)

        if (![System.IO.Directory]::Exists($gpoDir)) {
            Write-Warning "GPO backup directory missing for $gpoDisplayName; skipping"
            continue
        }

        Write-Debug 'Copying GPO backup directory'
        Copy-Item -Path $gpoDir -Destination $Destination -Recurse

        Write-Debug 'Appending GPO backup metadata to consolidated manifest'
        $finalManifest.DocumentElement.AppendChild(
            $finalManifest.ImportNode($_.Node.Clone(), $true)
        ) | Out-Null
    }
}

Write-Verbose 'Writing to consolidated manifest.xml'
$finalManifestFile = [System.IO.Path]::Combine($Destination, 'manifest.xml')
New-Item $finalManifestFile -ItemType File | Out-Null
$finalManifest.Save($finalManifestFile)