Hello, it would be a pleasure to help you with your request, surely, you should check if you have a firewall that prevents the connection to the TCP protocol that you have configured the RDP, additionally.
The first thing we would do, is to identify if the failure comes from the configuration of the rdp server, lan network or external networks such as vpn, I comment that as a security measure, it is always advisable to work with vpn, so that you can access the RDP locally and not by the WAN IP, as it is a security flaw for your server and your network in general.
In case you wish to work with another partner, you should also take into consideration these suggestions, so that you do not have problems with vulnerabilities.
Remember that it is not only about connecting devices and systems, but also about protecting them.
Have a great day.
Best regards.