My guess would be they're using some 3rd party library of "fake user agent detection", and this library just has a whitelist of what's "acceptable".

Given that the "fix" involves making the string reported "Possibly Apple, Possibly M1", I am going to say it's a blacklist.

There are two ways in which that could happen. Someone entered that combination into the list without thinking it though. Or more likely, they use a self-learning or heuristic filter that finds the combination 'Linux' and 'Apple M1' unusual because of how rare it is. Either way, it's easier to assume a mistake here because such a dark pattern doesn't make any business sense - notwithstanding their ethical reputation.

Sure, I doubt it's anything other than someone eagerly grabbing a list of long tail things and blacklisting them.

This is just a guess, but maybe "inconsistent" identifiers are a good signal of being an attack bot instead of a user.

Not defending that btw. Auto-generated signals are likely a problem for any desktop Linux user, not just Asahi, since most bots will run on Linux VPSs.