I think that those working in or at someone's home should try to avoid needing to use their loo where possible at the moment eg. If your gardener comes to you from his home or travels via his home, then mostly he won't need to ask you and it seems that he has hardly ever asked so I guess he usually avoids it. But there will be times people need cannot avoid needing the loo and I think you take that on when you hire them, you should provide that access. If you are shielding or cannot provide access you should mention this at the time of booking.
For people asking about the risks of going to the loo, obviously there are the usual risks from breathing, touching surfaces. They can be somewhat mitigated by providing a disposable mask and by cleaning afterwards. If you think a visitor will need to use your bathroom, remove any toothbrush, towel etc from near the loo before they arrive. Not everyone has a guest loo, we don't.
But there is also the issue of aerosolized virus particles from flushing...I wish it wasn't seen as awkward to ask people to put the fucking lid down. The virus is present in faeces ( and presumably urine, I don't know), and a study in Wuhan found that aerosolized virus particles were found in Covid patients toilet rooms in (I think 2-3 hours) after use, but not in their bedrooms where they were just breathing. Are these particles infectious...I don't know, it was not known at the time but probably is now if you look into it.
If you wait a few hours before going in those particles will have settled, but may still be infectious on surfaces.
My take on it is....if you have people at your home they may need the loo and you should let them use it, unless you are high risk and have advised them beforehand that there are no facilities. In that situation consider getting a portaloo if you need much assistance as it could be needed. If you aren't high risk just take some precautions before they arrive, have a clean disposable mask for them if you want them to wear it, ask them to put the lid down before flushing, and then clean in due course. If you cannot clean everywhere particles may have settled, then at least clean high touch areas such as handles, taps etc.
Hopefully, the chances of any individual using your loo having Covid are low so this is an abundance of caution, but still reasonable.