not OP either. but i think the problem is simple. apple said no to opengl, which any other platform out there supports.
btw, they are even deprecating opengl! i have no idea what that means for the tons of games written with an opengl backend. probably not an issue for the iOS ecosystem though.
no one in the SDL developer community tells you how to support metal or how to use it. instructions for MacOSX redirects you to another library, which has since removed their instructions.
And in case anybody comes in raving about how Vulkan isn't supported on macOS, that's fine, Vulkan-to-Metal compatibility layer libraries are available.
Well, Vulkan is also not supported on PlayStation, XBox, Win32 and UWP sandboxes, Android devices until Android 7, and until version 10 only flagship devices actually had any kind of proper support.
btw, they are even deprecating opengl! i have no idea what that means for the tons of games written with an opengl backend. probably not an issue for the iOS ecosystem though.
so that's what is going on...