It proposed China (only as part of P5) to be a guarantor but China didn't volunteered nor accepted such request.
There is a great rick, burden and responsibility to be a security guarantor and for China to become one then it must involved itself in the negotiations process of any deals.
China has made it pretty clear about the role of the UN Security Council on the Ukraine matter back in 2022. It is also unlikely that China wouldn’t be aware of these discussions. With the no limit friendship with Russia along with the Chinese diplomatic effort in 2022 with Ukraine and Russia (separately).
China believes that the UN Security Council should play a constructive role in resolving the Ukraine issue, and give priority to regional peace and stability and the universal security of all countries. Actions taken by the Security Council should help cool the situation and facilitate diplomatic resolution rather than fueling tensions and causing further escalation.
State Councilor Wang Yi noted that as a permanent member of the UN Security Council and a responsible major country, China has always faithfully fulfilled its international obligations and played a constructive role in maintaining world peace and stability. When it comes to peace and security, China has the best record among major countries.