They have an app which was up and running by April. Everyone had to download it - and they use their phones there for everything, including paying in almost all shops now, so it was a case of no Covid app, then no food, no entry to public buildings or transport, nothing. In fact in most places you wouldn't even have been allowed out of your apartment block without it. Add to this the fact that mask-wearing is very common and accepted there anyway, but it was made absolutely compulsory once lockdown was partially lifted. It's not mandatory any more, as far as I know, but a lot of people will still wear one voluntarily.
Also they closed the borders, and they've remained closed except for absolutely essential reasons eg medical personnel travelling internationally. I have an American friend who normally lives in China but who 'evacuated' back to the States in February (something he now deeply regrets!) and still can't get back. All his belongings and furniture are stuck in China and his visa has lapsed. Meanwhile there's no work for him in the US (which is why he moved to China in the first place). He doesn't know what to do.
But life in China has been back to more or less normal (albeit with the app, and a very strictly enforced quarantine system for those needing to self isolate) since really very early on - late April or early May. What you need to understand about China though is that people don't travel around the country much, apart from three times a year: once at Chinese New Year (which was largely the reason the virus first spread when it did, as fast as it did), once normally at the 'Tomb Sweeping Festival' but that's on April 4th/5th so I’m guessing that got cancelled this year. And the third time is during the National Week which is the first week of October.
If you look at any pictures taken over the past week or so (and I see a lot of them, mostly from westerners who live there) you will see that the movement of people around China this last week has been immense, even if it's slightly down on normal years. So what happens over the next two weeks in terms of infection rates will be crucial and very interesting to see.