AMD does offer custom x86 - see the steam deck, surface laptops and Xbox and PS4 and 5. Given there aren't a ton of small fish making custom parts they are excellent at what they are made for.
AMD is pushing x86 to Apple ARM levels that keep power use low enough (best I've seen is 16 hour battery life on a device - I think MacBooks best this still) but performance per watt I haven't seen ARM really top charts. They are awesome and I want arm and risc-v to really shine in laptops but the only player on the PC side is Qualcomm who was told to destroy their only flagship by ARM.
These sorts of processors are available from Intel as well (if anything, more available, as you can buy low-end 5w processors with modern e-cores in them, eg. N95/N97). The commenter above is referring to these, and they are common in Mini-Pcs with 8-16GB of RAM and cost <200USD. These sorts of processors crush the ARM competition at the same level right now (ie. the pi).
In fact, AMD doesn't seem to have anything in the same segment currently, although they do exist in the higher tiers alongside Intel with their laptop processors.
AMD is pushing x86 to Apple ARM levels that keep power use low enough (best I've seen is 16 hour battery life on a device - I think MacBooks best this still) but performance per watt I haven't seen ARM really top charts. They are awesome and I want arm and risc-v to really shine in laptops but the only player on the PC side is Qualcomm who was told to destroy their only flagship by ARM.