I had a recent reservation that cancelled and received a full refund 1 1/2 days before check in, claiming she has covid. I have no way of knowing for certain if she does or not, but just before she cancelled, she did send me a lengthy message with several questions about the cabin and was upset that she didn't notice these things when she booked. She did send a message about cancelling and she knew before hand that she would get a full refund.
So I'm assuming if someone wants out of a reservation, all the need to do is claim covid without any proof. Why do we have cancellation policies when it's that easy to get around it and pop-ups will remind them repeatedly of that fact. Does airbnb require any documentation of a covid diagnosis? I'm guessing no.