I think you missed it because of the "highlight unsolved numbers" option, which greys out numbers that have all their mines even if the rest of the squares aren't all open. I recommend you turn that off.
used to play that game 20+ years ago, idk if they made it guess-free now, but back then i would encounter this from time to time, at that that point it was about chances, in this case looks like 50/50
Yeah they make guess-free versions now. It's much more fun when you know that you're too stupid to finish it and it's not simply impossible! In a normal version OP would have probably guessed one at random fairly quickly, but here OP kept thinking "what am I missing?".