PowerShell limit self-built domain administrator account can only log on to the server operating system

PowerShell limit domain administrator account can only log on to the server operating system, built-in Administrator invalid.

Import-Module ActiveDirectory
$ADusername = 'domainadmin'
$complist = Get-ADComputer -Filter 'operatingsystem -like "*server*"' | Select-Object -Expand Name
$comparray = $complist -join ","
$Wks = (Get-ADUser $ADusername -Properties LogonWorkstations).LogonWorkstations
$Wks += ",$comparray"
Set-ADUser -Identity $ADusername -LogonWorkstations $Wks