I have noticed more people using FB less than before all this started, and friends I've spoken to have said they use it less for the same reason(s) the OP mentioned. Me personally, I haven't used it less, but I have had to remove a few people from my friends list who went down that same conspiracy theory rabbit hole or started posting pics/videos that are blatantly xenophobic (which of course is denied, and they insist it's because they "love Britain"), as well as those that just wanted to be particularly argumentative about COVID, BLM, Brexit, etc. So in a way I look at it as a good thing as you get to weed out a few of the rotten/rotting apples that can, if left unattended, start to impact your well-being. I feel fairly unaffected by it all mostly, although it is sad when it's someone you thought was smarter than that, and now probably won't speak to again...
EDIT: One of the thing's people have said to me they use it less for is because they feel that it's not representative of real life, and people only post the good things that happen and not when things go wrong or bad. That's something I'm aware of: people using it as a gloating/boasting platform, whilst hiding the less desirable parts of their life - which really isn't lying to other people so much as lying to yourself. I post anything and everything: from when I'm happy about the way things are, and how I feel, to when something's gone tits up or I'm not feeling my best. I feel it's important to maintain the balance and not just present a one-sided view of life, which really isn't the full picture.