@Elena646, I think @Emiel1 made an excellent observation: there are a LOT of AirBnB listings in Florence.
AirDNA counted 9,444 active listings.
Your listing is not really "at the very end of search results". When I managed to move the map so there was only 115 listings on the map, yours was near the top at #4. (Possibly because it still has the "New" tag on it.)
But there are so many listings in Florence that it is very hard to appear on the list at all.
You have Instant Book on, which helps a lot. The next most important thing is to get some good reviews... but you need guests to get reviews.
As suggested, perhaps you can promote outside of AirBnB to get your first bookings; once you have some good reviews from happy guests, that always helps your listing climb up the rankings.