There are well supported ways to keep using OpenGL on MacOS and iOS. This company is offering a wrapper that makes OpenGL run faster on top of Metal than it did natively, and promises support for future OS versions indefinitely..
So I suppose if Apple cared about not being hostile to developers they'd have the option of buying that company and giving the product away for free.
A company is selling a product that provides a clear value to a specific audience; they're likely to be far more responsive and effective than Apple could be.