flatten.ps1

$src = ".\goog"
$dest = ".\goog2"
$num=1

Get-ChildItem $src -Recurse -Include *.gif, *.jpg, *.jpeg, *.png, *.bmp, *.heic, *.heif, *.mov, *.mp4, *.webp, *.avi, *.tif, *.flv, *.mts | ForEach-Object {

    $nextName = Join-Path -Path $dest -ChildPath $_.name

    while(Test-Path -Path $nextName)
    {
       $nextName = Join-Path $dest ($_.BaseName + "_$num" + $_.Extension)    
       $num+=1   
    }

    $_ | Move-Item -Destination $nextName
}