We have the regulation government QR code check or sign in for contact purposes but it can't be policed.
Most of our guests assure us they have been double vaccinated like us, some with boosters. However, we have a regular anti-vaccine guest, a health professional but it is her problem if she gets the virus, not Airbnb's, us or anyone else. We limit contact with her and follow the Airbnb cleaning and sanitising except for masks and pp covering which is not required here with no local cases. She runs a small business while here and if her clients are infected then that is also her problem.
It would be a nightmare to keep a vaccination register of all guests, visitors and tradesmen if needed so unless Airbnb wants to do this we don't.