Hi @Andrew-And-Moragh0 , I've spent a bit of time figuring out the rules and implications of this, because we wanted to do the same thing.
My understanding is that AirBnB hosts can ask ask for vaccine passes, just like other types of accommodation providers. You can do this at all 3 traffic light settings
There's good information here (https://covid19.govt.nz/traffic-lights/life-at-red/travel-and-accommodation-at-red/accommodation-at-..., or see the page for accommodation at Orange) and here (https://www.business.govt.nz/covid-19/covid-19-protection-framework/accommodation-services/)
However, if you allow instant bookings but you want to cancel a booking because someone fails to prove they're fully vaccinated, it WILL affect your hosting stats and rankings.
That's because AirBnB currently doesn't consider it to be a legitimate reason for a host to cancel a guest's booking, even if you clearly state in your House Rules and listing details.
So we've turned instant booking off, and require guests to send us a copy of their vaccine passes if we accept their booking (unfortunately you can't do this before you accept a booking, because you can't share links and images via their messaging system before then).
Frankly, it's a bit of a pain in the proverbial, 'cause it's taking more time and effort.
I prefer Bookabach's approach: they've told us we can cancel instant bookings if guests don't provide proof of vaccination.
Hope this helps. Sing out if you have any more questions.
Regards Patric