Right, you need to check the logs on your router.
Is it blocking some inbound packets when you try and connect?
I assume you can connect locally? i.e. inside the router? To the local private address.
If it works fine internally then try from outside and then check the router logs. Obviously you’re looking to see what traffic gets blocked if any.
You might want to try some low level tests too, see if you get a response when you telnet to your server on port 1723.
i.e. from a command line, telnet 1.1.1.1 1723 (obviously 1.1.1.1 will be whatever your public address is)
If it were me and I were looking to connect to a windows machine remotely, I’d use the built in VPN on the router, which will be an IPSEC one. If it didn’t have one, I’d get a new router.