At this point it’s more about the symbolic victory for propoganda’s sake with a recent tide about other emerging or fully authoritarian states eyeing up their neighbors based on historical grievance culture

Iran over Mesopotamia and the Levant, Azerbaijan and Armenia/Northern Iran, Israel and everything between the Nile and Euphrates, Argentina and the Falklands, Ethiopia and everyone with coast access in their vicinity, Venezuela and Esequibo, Turkey and Northern Syria, and most importantly of all for Russia now, China and their own irredentist territorial claims.

China backs Russia because a successful forced recognition of the annexation of Ukraine in whole or in part sets precedent that Beijing should be allowed to do it to Taiwan if they win an invasion and establish an occupation. What Beijing is actually betting will happen though, is that Russia is going to blow itself to pieces against Ukraine, allowing them to establish a much harsher grip in future negotiations they want to settle, like access to Lake Baikal, or Siberian natural resource wealth, or cheaper fossil fuels, or probably what Beijing sees as their own grand prize, quelling the Taiwan fervor among their population by instead extorting a return of the former lands of Manchuria which Russia took in its own unequal treaties with China.