In reply to Flinticus:
I've been five or six times. First time, like you, I was not sure what to expect (mostly from my own feelings rather than any perceived scenario) and decided that if I felt uneasy about anything, I could just walk out. It was fine. As Lrunner says, better than (say) a coffee shop. Cineworld (and Broadway cinema in Nottingham where I went to see First Cow) have a policy that you must keep your mask on during the film, unless eating or drinking (kerCHING at the sweets counter!) and at Cineworld a staff member comes into the screening two or three times and checks the audience (presumably for mask compliance) using night vision goggles (which has the side effect of deterring me from sneaking in a cheeky beer!
All that said, I haven't been to any busy screenings and Cruella is the only "big film" I've seen (and I strategically chose a 17:10 screening as that is a kind of "dead zone" time. Other films have been Nomadland, Frankie (members-only early preview), Judas and the Black Messiah, Those Who Wish Me Dead, A Quiet Place Part 2 (members-only early preview) and First Cow. These are not films that really attract troublemaking anti-mask "rebels"....
The only time there was anyone within even a row of me, was Cruella, where I had four young women sat behind me. They behaved impeccably. If I hadn't felt comfortable, I could have moved forward a row.