It's quite apparent to anyone who has lived there for a while and talked to people. Some large scale anonymous surveys done by not particularly sympathetic outsiders also confirm it (e.g. https://www.washingtonpost.com/news/monkey-cage/wp/2016/10/0...).

That's what happens when the party controls information to paint a very specific picture. You'll find that anonymous surveys in DPRK will also show that most support the Kim regime.

What became the Chinese government we know today also conducted "anonymous" surveys during the cultural revolution. Those who answered incorrectly were bundled up (along with their families) and never seen again.

> How would one know if the Chinese government was supported by the population or not

Or given the fact that any attempt to gather opinion about the communist party on the ground would instantly land you in jail, this is an impossible statement if anything.