Edited to add: The info below applies to the booking.com website seen by people in the US.
I don't know when this started, but the lodging rates shown on the initial search-result screen on booking.com now exclude VAT as well as the city tax. City tax in places like Italy, where it commonly must be paid directly to the hotel in cash, has always been excluded, as far as I know. In the past, VAT was included. The initial screen does not mention the exclusions; they are noted (and percentages/amounts shown) when you click through to a specific lodging place.
This is something to pay careful attention to as you compare booking.com rates to rates on the hotels' websites (which I guess may or may not include VAT, depending on hotel policy).
I notice the change when hotel-shopping in Venice and verified the same pattern in Sarajevo, Berlin and Malaga.
Another tip: It's worth checking the booking.com app, which may have a lower price than the website.