I believe the whole reason China tolerates the Norks is that they are communist and in between them and US troops. Which is to say it’s a lot easier for all concerned to care less: the NORKs serve a purpose to the. ChiComs without being vital.
I’m guessing that if they do anything it will be to either rope in Kim or replace him with communist junta more agreeable to the purposes of the junta in Beijing.
But China has been trying to get friendlier with South Korea, they know in the long-run South Korea will prevail on the Peninsula. That’s why their best possible outcome is to make a deal that let’s the South be comfortable with kicking out the US. That’s what China really wants, the US gone from the Peninsula, one way or the other.