$portvalue = 3390

Set-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp' -name "PortNumber" -Value $portvalue

New-NetFirewallRule -DisplayName 'RDPPORTLatest-TCP-In' -Profile 'Any' -Direction Inbound -Action Allow -Protocol TCP -LocalPort $portvalue 
New-NetFirewallRule -DisplayName 'RDPPORTLatest-UDP-In' -Profile 'Any' -Direction Inbound -Action Allow -Protocol UDP -LocalPort $portvalue

reference: https://learn.microsoft.com/en-us/windows-server/remote/remote-desktop-services/clients/change-listening-port