That's a complex question, again the long answer is no. Both MoltenVK and the gfx-hal portability work (from Mozilla) allow you to run Vulkan workloads on Metal, thanks in large part to spirv-cross. I also see ~WebGL~ WebGPU on the horizon, and Apple is a very active participant in that process. Code written today to run on Vulkan, using any language that compiles to SPIR-V, will be pretty easy to adapt to the WebGPU future.