It’s not a huge deal in the first place. Still a strange situation. Is there a fix or a way to force G-Sync?

Just in case you mean v-sync...

In this thread -> https://www.gog.com/forum/battletech/100_gpu_usage
a user named -> bellastrega
said he used his video card control panel "to set v-sync globally to "on"".

I believe that I've run into some advice from HBS that suggested doing this but I could not find it easily and gave up at this point.

Thx for the reply, but I really meant G-Sync :)

The two issues are probably related.

Have you tried to override application settings using the Nvidia Control Panel?

Yes, that was one of the first things I did.

But I've found a solution (after a day of research): The game has to be set into exclusive fullscreen mode, you need to start it with the following parameter:

-window-mode exclusive

G-Sync works now :)