I went in 2018 and spoke with some of the employees working there. It’s very true. Almost no one lives in the city proper anymore; everyone commutes from outside.
On a related note if you decide to go: the city proper is very much a tourist trap. The food is not good and everything is overpriced. If you decide to go I wouldn’t spend more than a day inside the city itself. I had a much better experience taking the water taxi to the surrounding islands. The food is better, people are nicer, it’s way less crowded and the sights are just as good.
Now around 50,000 people live in Venice. It not so empty.
In Rome, Florence it is the same a lot of people have moved in the suburbs. Mestre, the city near Venice, has 88,552 resident.
I lived in Venice for about 30 years.
On a related note if you decide to go: the city proper is very much a tourist trap. The food is not good and everything is overpriced. If you decide to go I wouldn’t spend more than a day inside the city itself. I had a much better experience taking the water taxi to the surrounding islands. The food is better, people are nicer, it’s way less crowded and the sights are just as good.