I haven't seen this discussed here (apologies if this is well known & I missed it) but I thought I'd share a bit of our experiences trying to book a few nights in London for this May.
We'd spotted a couple of nice-looking candidates on AirBnb (good location & reasonable rate) and the calendar showed availability. Yet when I made an enquiry it either went unanswered or showed in my message queue as 'unavailble' (with no contact from the host). From other experiences, this was not at all typical -- I always hear something back.
Then, one of the hosts replied, "Yes, it's available but we reached the 90 night limit...."
What?! So, of course I had to google to see what this was all about. And I found the explanation fairly easily. Here's one of the best recaps (albeit by a party with an acknowledged bias):
https://www.airsorted.uk/blog/90-day-airbnb-rule-and-what-it-means-you/
Here in Hawaii there is also a lot of back-and-forth about this 'new' (or not so new, depending on your age ) mode of vacation lodging and how it is being received (or fought). In that light, this was an interesting read.