Just adding some extra context.
Hosts must register guests to "Guests portal" in the official Police website https://alloggiatiweb.poliziadistato.it/PortaleAlloggiati/ so guests information is required. Hosts should check your ID upon arrival and insert those information in the "Guests portal".
It is illegal to ask for documents through email or photograph/...
In Italy, there is a legal requirement that all guests of hotels, B&Bs, rooms, etc. (including Airbnb) must be registered with the local police, so I guess it's not a matter of tourist tax but they are asking it because of this registration.
In the most recent version of the law, the host must fill in an online form to register the guests. From what I ...
I contacted the Airbnb support before replying to my host.
They called me in an hour, confirming that I need to provide copies of our IDs as the host needs to file for tourist tax with them in the local police department or something like that.
They assured me that it's needed and there's no way around it. Especially if I am not meeting the host in person.