Nothing happens in China without government support. In China you either do what the government wants or you are in jail or dead.
If Xi wanted Russia to stop the war, Russia would stop the war. The war is useful for China because it splinters the west, they get leverage over Russia, and it normalizes the kind of actions that it wants to take in Taiwan.
If China objected to North Korea sending troops to Russia then North Korea would not be sending troops to Russia. Pretty much all of North Korea's trade is with China. For sure North Korea has some degree of independence but sending soldiers to die for Russia is not worth it if it upsets China. This is clearly a nod, nod, wink, wink situation here.
"Most of Russia's exports to China originate from the mining and petrochemicals sectors.[64] More than half of Russia's exports to China come from mineral fuels, oil, and petroleum products (60.7%), followed by wood and wood products (9.4%), non-ferrous metals (9%), fish and seafood (3.5%), and chemical products (3.3%). China is also gradually becoming a major consumer of Russian agricultural products.[24]: 64
The main categories of imports to Russia from China are machinery and equipment (35.9%), clothing (13.7%), chemical products (9.1%), fur and fur products (5.6%), footwear (5.3%), and furniture (3%). Chinese electronics are steadily expanding their presence in Russian.[24]: 64"
https://en.wikipedia.org/wiki/China%E2%80%93Russia_relations...