ARM is not a GPU-architecture, but a competitor to x86, which is what intel and AMD are basing their CPUs on. Through a very confusing web of patents and deals, only those two corporations are able to use it. ARM was developed to be slimmer than x86, but only recently cought up in performance, while retaining an advantage in efficiency. They're not compatible with each other though, which is why apple had to create an emulation layer for x86 software when they switched from intel to arm for their cpus. Microsoft will (and have) need to do the same thing, but it's not clear yet what performance will look like for things like gaming. Microsoft largely want to make windows on arm a thing for battery life and so that they can create their own processors.