Peter Zeihan said they wouldn't dare do it because Russia made clear they'd get all out nuked for it. Also, there is nothing really to gain but shithole territory.
China is smarter than Russia and successfully is conducting soft annexion during long years...
China does have approx 10 times higher mobilization resources than Russia and for them Russia is " small country " for conventional war.
China also might easily nuke Russia and will not fear from empty talks. China is nuclear power and unlike pussy westerners might really launch nuke if Putin will get not cooperative.
Also China is very important supplier of machinery etc, also very important rare earth metals producer...in some rare earth metals Russia can't replace supplies from China....
Putin's small special operation in Ukraine is very good for China to do soft annexing physically and financially.
For example when russian speakers in Siberia are busy with special operation in Ukraine, replacement in Siberia is needed, so immigrants are needed in order to have workforce and businesses....
Mandarin speakers might be protected with nukes China does have and historical territories might get reclaimed even in conventional war.
Also China advocated 1 child policy only for chinesse in China. If they are located in foreign countries then the more kids then better.
Russia doesn't knows that countries like Pakistan, India, China and Iran does have higher mobilization potential than Russia and countries like Pakistan, India and China might nuke them if will be too much triggered. ..they aren't Biden in white house.