if I pass focus during a showdown and my opponent reveals zhonyas as a reaction to my action speed spell, does zhoynas resolve. is there a window for me to play acceptable losses before the showdown ends

Yes to both. Zhonya's resolves — permanents played from hidden resolve as soon as they're finalized onto the chain, with no window for anyone to react to the reveal (FAQ #7377, #8213).

Then, once that chain finishes resolving, focus passes to the next player in turn order, so you get another focus window before the showdown can end. The showdown only closes when all players pass focus in sequence (Rules 347.2.a, 348) — passing once doesn't lock you out.

That next window is exactly when you play Acceptable Losses: it's an [Action] spell, so it's legal during a showdown, and it doesn't target — each player just picks a gear to kill at resolution, so it can freely blow up the Zhonya's that was just revealed. The only case where focus wouldn't pass after the chain is if the chain opened from a triggered or [Add] ability (Rule 346.1), which isn't what's happening here.