To be clear I agree that OpenGL is old and there are newer options. Still, if you want your C code to work on iOS/android/mac/windows with little modifications, still OpenGL is the way to go. I actually wrote such code that its used on a iOS app and Android app, and I am using the same code for a level editor that is running on mac and windows(some of our content editors don't have MACs). A lot of people ignore the fact that if you want to go for a multi platform approach, developing separate graphic pipelines would incur great costs. In my case I would have needed to write the same code 3 times in different APIs(I suppose Metal on iOS and Mac is about the same). Maintaining that separate pipelines would also be challenging incurring more costs. Still if you are just starting your multi platform approach, I would suggest to have a look at the 3D engines already available, for example Unity or Unreal engine(those 2 have some licensing costs but I think it's worth it). Those engines usually handle the graphics API stuff and you don't have to worry about OpenGL/Metal/Vulkan/Direct API etc. and you don't have to worry about Apple removing OpenGL because they will handle this(to be fair they are probably already using Metal).

Come on Apple stop wasting your developer's time. This is not the first Xcode update I have this issue just fix this please.