Alyssa chooses some very odd language here, it seems to me. Yes, Apple GPUs do not support geometry shaders natively because geometry shaders are a bad design and do not map well to GPU hardware (geometry shaders are known to be slow even on hardware that allegedly supports it — there is a reason why Nvidia went ahead to design mesh shading). Transform feedback (ability to write transformed vertex data back to memory) is another feature that is often brought up in these discussions, but Apple GPUs can write to arbitrary memory locations from any shader stage, which makes transform feedback entirely superfluous.
The core of the issue is that Apple chose to implement a streamlined compute architecture, and they have cut a lot of legacy cruft and things that were known not to work well in the process. I don't think that the rhetorics of "M1 getting stuck at OpenGL 4.1" is appropriate. I stopped following OpenGL many years ago, so I don't know specifically which features past 4.1 she might refer to. What I can say is that I'd be very surprised if there is something that OpenGL offers that cannot be done in Metal, but there are plenty of things possible in Metal that cannot be done at all in OpenGL (starting with a fact that Metal shading language has fully featured pointers).
The core of the issue is that Apple chose to implement a streamlined compute architecture, and they have cut a lot of legacy cruft and things that were known not to work well in the process. I don't think that the rhetorics of "M1 getting stuck at OpenGL 4.1" is appropriate. I stopped following OpenGL many years ago, so I don't know specifically which features past 4.1 she might refer to. What I can say is that I'd be very surprised if there is something that OpenGL offers that cannot be done in Metal, but there are plenty of things possible in Metal that cannot be done at all in OpenGL (starting with a fact that Metal shading language has fully featured pointers).