An employer can legally deny just about anything that they consider 'unreasonable', yes. If you injured your back and could no longer stand for hours at a time on a job that requires it and there is no alternative, absolutely you can be let go.

Picking out WFH as 'not protected' is largely meaningless. This is why it is called _reasonable_ accommodation, not _required_ accommodation.

As with any job, how you do your job, where you do your job, etc. can change based on the number of farts the CEO has passed today.

Yes, worker protections in the US are abysmal. You'll never find me arguing otherwise.