I am not sure if I understood it correctly, but OpenGL is high-level like Java and Metal is low-level like Assembly, aren't they? Apple seems to have abandoned OpenGL in favour of Metal, but there still are a few popular applications that use OpenGL like Blender. I think I have read that because of Apple's lack of support for OpenGL, Blender development is hindered.
Then, I wondered if some developers could implement an OpenGL library using Metal, and Blender could use that library. Then the developers of individual applications like Blender would not have to waste their time rewriting the applications in Metal. Is that kind of library plausible? I have searched Google for that, but all I could find was an OpenGL-ES-to-Metal project. I don't know whether OpenGL and OpenGL ES have similar architecture or not, so I am not sure the existence of that library means such a library for OpenGL is possible or not.