Their supply chains are quite globalized.

There have been mobile competitors like Imagination, but the reality is cutting edge chip design is enormously expensive and hard, and there’s a big performance gulf. Imagination (and others) can’t afford to fab their own designs, and no one takes them up on it unless it’s a mobile chip or something.

SiPearl was working on a rather massive ARM CPU: https://www.anandtech.com/show/16072/sipearl-lets-rhea-design-leak-72x-zeus-cores-4x-hbm2e-46-ddr5

Looks like the effort is still alive, but it was focused on server stuff and compute.