Peter K

Thank you Chris for the response. If you want to follow system behavior, application without focus should have darker UI with grayscale icons (macOS Monterey). I think that older versions of macOS use different approach, but I'm not sure right now. However, if your products use custom UI theme, you could implement the latest modern behavior. Or just don't change UI colors at all (many 3-rd party apps do that).

I prefer to use light UI on macOS and I must say that version 2 has lots of serious issues with this option. It looks like nobody bothered to test it.
Different UI brightness right after setting light UI and after swithing to different app and back. Too dark background of selected buttons – bad contrast with icon. Too dark backgrond of all buttons actually. Hard to distinguish between normal state, pressed and disabled. Select boxes have dark background, they look like disabled. (Input boxes are white) All icons on buttons are flat with very low contrast. (Icons in dark mode are much more colorful with 3D effect.) Overall it is so bad that it forces me to use dark UI instead. Version 1 of Affinity products do much better job in UI usability.