Well that's the thing with iOS -- the gamemaker compile doesn't produce any errors, it just generates the XCode project.
If I look at the XCode report navigator, there are a ton of warnings, but only one error. It says
:-1: symbol(s) not found for architecture arm64
/clang:-1: linker command failed with exit code 1 (use -v to see invocation)
GMS2 doesn't require XCode 11, does it? Cause I just have High Sierra and can't upgrade to Catalina because of all my old 32 bit apps.