@Terrill0 I'm not sure what the problem is. Certainly, if unsure of vaccination status, don't share a bathroom unless cleaning in between uses and limiting close or unmasked contact while accessing the bathroom. However, given what we know now about the likelihood of spread in an outdoor environment, I'm not sure what your concern is there.
If you have doubts or are unwilling to ask your guests about their status, then mask up when interacting with them.
I don't think asking is a problem. I think that making their stay conditional upon a vaccination is the problem, although ultimately it should be up to the host. It's also an honor system. A verbal yes or no will have to suffice, rather than asking for proof with a vaccination card.
I mention my own vaccination status in my check-in message and now in my listing, and most people respond with theirs, although I do not ask. I simply open the door.
I think here in the US in certain areas, we've gotten comfortable with being vaccinated and making assumptions about the vaccination status of the general population. I'm comfortable welcoming guests because we interact outside. I still wear a mask in public, mostly to be self-righteous (ha!), partly to set a good example, and also because some vaccinated people have gotten sick with the Delta variant, although not as sick as they might have gotten without the vaccination.
I suggest mentioning your own status in your listing or in your messaging, without demanding anything of your guests. You may be pleasantly surprised at what you find out. Good luck.