Just an idea as I don’t know what your network setup looks like…If you have a separate guest SSID (and therefore a separate subnet) then what you could do (and what I plan to do) is set up Trusted Networks, more specifically the ‘trusted users’ aspect of that.
So create a user called “Guests” to control a wider area of the house or to be more specific (allowing them to choose) create users like “Bedroom 2”, “Bedroom 3” etc. and then with trusted networks set that subnet’s trusted users to be your guest subnet only. Then you build a specific dashboard just for your guests to see and (the only way I can see around this at the moment) make all other dashboards “admin only” so that those users will only see the guest dashboard.
So to build on what @Skye has said about mDNS, you ask them to connect to your guest SSID. You then say go to guestroom.house where it’ll ask them which user they’d like to log in as - They select “guest” and that’ll present them with a Lovelace dashboard that you’ve setup that only the “guest” user can see!
I haven’t put this in to practice yet so cannot fully attest to it working but (I think) the theory is sound…Someone is of course free to tell me how wrong I am!