Also there is a lot of stuff on macOS that has been deprecated for ages and still works just fine. I don't expect OpenGL to go anywhere for quite some time. We just have to accept there will be no more features than we currently have. With the lack of updates we have seen over the years since the introduction of Metal we kind of expected this, right?
Yes, I have been dreading this stupid move for years. It's not even the first time Apple has made this stupid move, trying to push their own 3D API when they really should not be.
As far as no features... Apple has already not updated OpenGL significantly for many years. I see this announcement as more than that, as signaling a future (indeterminate) removal of OpenGL. When Apple makes a public show of deprecating something and telling devs not to use it, it means more than they just aren't updating or supporting that thing-- it means that at some point in the future, that thing is going away entirely. What would be a mistake would be to keep on as is assuming that MacOS' already anemic support for OpenGL will remain.