Do people go to see Venice, or to see Venetians?
The easy, facile answer is to move all the residents out, turn the old city into Historic Venice Amusements District, build a commuter transit line out to New Venice (with no tourist attractions), and all of its civic services are then paid for by income from the tourist trap. Everyone has ready access to service jobs in the tourism and public safety sectors. If tourists want to see real Venetians, they pay to bring some in on the train, to be photographed in a nearly-authentic setting.
"Nobody goes there anymore--it's too crowded."
You shouldn't curse your own success. Plenty of cities would dearly love to have throngs of visitors that seek only to look around, have fun, eat, drink, and otherwise spend their vacation money. I know of one in Florida that was specifically built, from the swamp up, for that single purpose.
If you don't want all tourist attractions to become Disneyworld, you have to visit places that aren't yet well on their way to that endpoint. There are many places on this planet that are fun and interesting for visitors. I can very easily choose to no visit locales that have been overrun and ruined by overtourism. It's not difficult. If an underemployed local is trying to sell you discounted show tickets or pass out ad-laden maps of local attractions, you're in one. If your hotel has posted a warning about pickpockets, you're in one. If you can't discern the boundary line between the gift shop at the exit to the last attraction and the gift shop at the entrance to the next one, you're in one.