For those who say the seat next to them is selectable, did you check that when not logged in as a 1K (because of course you can choose that seat yourself if you want to). I see a couple of other posters say that United doesn't block next to 1Ks anymore, but they certainly have for me, every time. Now up until COVID-19 hit, that usually didn't mean much because once the plane gets full they (naturally, and as they should) override those blocks. But I know for a fact that the seat next to me has been blocked repeatedly over the past few years.

Edited to add, isn't it possible that some blocked seats on aircraft currently are due to "social distancing", as ridiculous as that concept is on an airplane?