ANGLE is the base of the WebGL implementation in Chrome. For WebGPU, we (Google) are working on a new native library called Dawn[2] that will fill the same role that ANGLE does for WebGL. I'm personally hopeful that Dawn itself can eventually be useful as a cross platform graphics abstraction for native apps as well as web apps. There's also Mozilla's gfx-rs[3] in the same space.
[1] https://github.com/google/angle
We still don't know when Apple will actually remove GL from their platforms, but since the backlash will be so huge, it might be a while. And even when they do, the first step of 95% of code-bases that rely on GL will be to link in some GL on Metal emulation library. The net effect will be a slight performance drop for Apple vs other platforms. Well done Apple.
At some point switching to Vulkan (and Vulkan on Metal for Apple, or the reverse if you're an Apple centric developer) may be worth it, but for the moment the amount of apps and games that will see close to identical performance in GL and Vulkan is still huge. If you are e.g. geometry/shader/memory bound, you'll see exactly 0% speedup from API changes. You really need to be pushing significant amount of draw calls to see a difference. If you're not doing this, its worth "hanging in there" with GL to see if the post-GL landscape de-clusterfucks itself in the meantime :)
Even on Mac OS it wasn't available, rather Quickdraw 3D was the API to go to.
Had Apple been successful with their in house OS, and surely they wouldn't have cared about OpenGL.
WWDC 1999: Mac OS 9 - A work in progress https://youtu.be/LkmSrCsKPLk?t=1360
Also note that Copland did not have any OpenGL support planned.