Actually, I expect that to not happen at all. Jurisdictions in the US already started to exempt FOSS OSes from age restriction stuff.

But if they actually try... look at how well prohibitions worked in the past - even when the prohibited thing was legitimately harmful and outlawing it made actual sense. When there is demand there will be supply. You can still get the absolutely worst drugs in the US. Surely it would be easier to get unlocked CPUs into that country than deadly drugs.

And if it really became impossible to get western CPUs that can run Linux inside the US... I could still just switch to Chinese hardware because like most people I luckily am outside the US. China is catching up.