Microsoft : Change Remote Desktop port

 The step

1. Start the registry editor. (Type regedit in the Search box.)
2. Navigate to the following registry subkey: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp
3. Find PortNumber
4. Click Edit > Modify, and then click Decimal.
5. Type the new port number, and then click OK.
6. Close the registry editor, and restart your computer.

 

Check the current port by running the following PowerShell command:

Get-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp' -name "PortNumber"

 

To add a new RDP Port to the registry:

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

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