It's not practical to have direct support for Metal because nobody who wants it is volunteering to write and maintain a new backend for it. Godot is a project

It's not practical to have direct support for Metal because nobody who wants it is volunteering to write and maintain a new backend for it. Godot is a project with limited resources and the Vulkan backend works fine on Apple platforms through MoltenVK, so as far as the people doing the work are concerned there's little point in adding Metal support and lots of other things are higher priority.