A while ago, it was peculiar when Apple declined to support Vulkan. Now they're deprecating support for OpenGL, OpenGL ES, and OpenCL, and both on Mac OS X and iOS. Instead, they want developers to use Metal.
That's pretty much the end of cross-platform support for anything GPU-related. Now you get a choice of supporting Apple OSes or supporting everything else. If anyone out there finds that a non-trivial decision, I'd like to recommend going with "everything else".