You either have the wrong resolution ingame - so double check that you are using the same one as the one in your windows display settings - or there is some other program causing issues for you in the background.

Try changing to fullscreen mode to see if that helps in settings - graphics - Window mode

My resolution hasn't changed in years. I am already using full screen. The only thing that changed is I downloaded the latest release and DLCs.

Can you check your antivirus/firewall? Now that the game has gotten an update and thus a new signature, they might have started blocking some gamefiles.

Could you also try verifying your game files to make sure nothing went wrong with the installation? right click Medieval Dynasty in the list of games in your Steam library, pick 'installed files' and then 'verify integrity of game files' and afterwards restart your PC.

Do you still have it afterwards?

How would any of that be the root cause of the issue? There is obviously a bug in the new release.

I'm going to have to put it in the list of "annoying things that make Medieval Dynasty aggravating" like having to chase arrows downhill.