sorting an array to find the longest folder path

Why sort at all? Sorting involves a lot of comparisons over and over again to insert the elements correctly. If you just want a list of problematic files you can do:

$RootFolder = Show-PWFolderBrowserDialog

$Docs2Export = Get-PWDocumentsBySearch -FolderPath $RootFolder.FullPath -GetVersionsToo -PopulatePath

foreach ($f in $Docs2Export) {
    if ($f.fullpath.length -ge 240) {
        write-host "$($f.fullpath.length): $($f.fullpath)"
    }
}

Why sort at all? Sorting involves a lot of comparisons over and over again to insert the elements correctly. If you just want a list of problematic files you can do:

$RootFolder = Show-PWFolderBrowserDialog

$Docs2Export = Get-PWDocumentsBySearch -FolderPath $RootFolder.FullPath -GetVersionsToo -PopulatePath

foreach ($f in $Docs2Export) {
    if ($f.fullpath.length -ge 240) {
        write-host "$($f.fullpath.length): $($f.fullpath)"
    }
}

Or something like this will work as well.

$MaxLength = 240
$Docs2Export = Get-PWDocumentsBySearch -FolderPath 'PowerShell' -GetVersionsToo -PopulatePath | Where-Object { ($_.FullPath).Length -gt $MaxLength }