We have news for ye olde Kingdom: New Lands on thy Macintosh computer. Apple dropped the 32-bit app compatibility with their release of macOS Catalina 10.15 (see their article here) which affected Kingdom: New Lands. Do not fear, we have good news, we have updated the game and added 64-bit support. That means you can play Kingdom: New Lands on Macintosh no matter if you run older 32-bit version or newer 64-bit version of macOS.
The update should happen through the Steam client. In case it doesn’t work, you might want to start with verifying your local files. If that doesn't work, uninstall the game and download it again through the Steam client. This should not delete your current save files.
Once more, venture forth and be brave, ruler, and fight to the bitter end,
lest these New Lands conquer you instead.