I also experience this annoying issue. Found this interesting precision on StackOverflow: https://stackoverflow.com/questions/68584885/how-does-xcode-decide-what-preprocessor-macros-and-other-build-settings-to-use-f

I encountered the same issue (previously using both background and background-darkAqua) and just found out the solution: make sure each one of them reference a different image file. Like so: <background file="background.png" mime-type="image/png" scaling="none" alignment="left"/> <background-darkAqua file="background-dark.png" mime-type="image/png" scaling="none" alignment="left"/> Hope that helps.