I've tried to setup a Remote Desktop session (I've used Chrome Remote Desktop and TeamViewer - always in Remote Control mode) where I and my friend can play Warlords2 each of us sitting at their own place.

To play it on one computer I use DOSBox 0.74 and it works fine, we had to meet in person but it was fun from time to time. Now we have the Corona-pandemic and it's difficult.
I was then thinking of a game played via kind of remote desktop. So I tried to start a game on one computer and then get a remote control conection with my other computer (this is the only way I know to enable remote control over an application). To some extend it works - the keyboard works OK.
But the mouse is lost and is moving only on the edges of the DOSBox window with the game session - there is no control over the game from remote control.

Do you know a way to fix it? Or can you recommend a remote connection app that could work for me?

At work I use Skype but it's commercial skype for business, where you can share your desktop or an application run on your desktop - I think something like that could work but I can't test the Worlords2 with my work computer.