Just to add some more info from a nearby city to Shanghai. In Suzhou, schools run programmes for the preservation of the topolect, they also have 苏州话 in some of the busses that go around the city centre. There’s even a Wu language section in the Suzhou library. Of course, with anything in the PRC every municipality will be different, but at least there is some preservation going on.

Though, according to this source (in Chinese) from 2022 only 2.2% of 6 - 20 year-olds can use 苏州话 proficiently.

The author does say they are unclear about how that data was gathered, so it could just be a limited amount of people from the Suzhou area gave a response. Still, from personal experience I don’t think it’s that low, as I’ve had several students (and some colleagues, though that would break the 6 - 20 year-old limit) claim that they spoke 苏州话 with their parents or grandparents.