The assumption is x86 will remain competitive for years to come, but that seems a lot less clear now. It feels like what ARM is doing right now is quite similar to what x86 did to mini computers and mainframes.
ARM has become a competitive pressure that will prevent Intel and AMD from cashing in on that platform the way they have in the past. Chromebooks and the iPad have been nibbling at the low end for a few years now. Now Apple's M1 is taking a big chunk out of Intel's lucrative ultrabook market. Microsoft and other OEMs are going to start pushing harder on ARM just to stay competitive.
Though being the sole licensee of x86, maybe AMD can pull a weird rabbit out of their hat.