You can see whether the remote desktop is allowed by the firewall by opening the Windows Control Panel , then clicking on the Firewall icon and on the text Allow an app or feature through Windows Firewall .
The direct execution / opening of the firewall settings works with firewall.cpl and it works on all Microsoft Windows operating systems Desktop and MS Web Server 2019, 2016, ...!
2.) Example Fritz box and the port release / forwarding for internet access!
Port forwarding on the FRITZBox is so easy that it hardly needs to be mentioned, but if you have never done the port forwarding. Here is the quick setup of port forwarding for remote desktop in order to be able to access the home PC from the office, or vice versa!
1. Open the Fritzbox user interface.
2. Navigate to: Internet ► Approvals ► Port Approvals.
3. Click on "Add device for shares" at the bottom right .
4. Now simply select the PC / smartphone, ... (point-5)
5. Now you can share a network device
(in this MS-Remote - desktop)
6. Confirm with [OK]