Apple say that Apps built using OpenGL ES will continue to run in iOS 12, but Open GL ES is deprecated in iOS 12. Games and graphics-intensive apps that previously used Open
I recommend that OpenGL and Metal are developed together on iOS, and new features are used with Metal.
You more or less do not.
Apple has made it abundantly clear that they are not interested in supporting OpenGL ES further on any platform they control. In the future, you will use Metal or you will not have accelerated 3D graphics. Those will be your options.
There are projects that expose OpenGL ES on such platforms by implementing an ES layer on top of Metal. MoltenGL, for example, but that one isn't free apparently.