Europe varies a lot from largely cashless to you will probably need cash if you want to have a beer.

it's even more intense in China

What is more intense than nobody taking cash, punishment for even having it?

Your ability to make purchases turned off, with no other means to transact.

https://en.wikipedia.org/wiki/Social_Credit_System

as in it is very difficult to find anyone willing to transact in cash for any transaction whatsoever in most chinese cities

Not even big cards like Visa or Mastercard work everywhere.

Instead you need an app installed on your phone (alipay or wechat), where you transfer cash into the app in advance. All with Chinese as the only language. (From what i heard, there now is a tourist-version of alipay in English. Last time i tried it was mostly Chinese)

honestly it was pretty intuitive even when navigating all in chinese

Don't the public restrooms take coins there?

Public restrooms in Czechia often can take cards now. I imagine it works similarly in Sweden.

As an American, this concept still makes no sense to me. It's public infrastructure of a sort, don't real estate taxes in the surrounding area pay for upkeep and repairs?

See also, subway stations in Japan, which IIRC operate under a similar model.

Transit is so good it replaces cars. That means users can afford to pay for it.

Free transit is a terrible idea because e.g. it means tourists don't contribute and anyone who passes a tax cut will have defunded it without the actual users being able to help.

How does this account for people who live paycheck to paycheck and don't have cars?

This is literally how they get around - asking those who can pay the fare to subsidize them doesn't seem like that much to ask.