It isn't at all the same. Which country is going to recognize or absorb Xinjiang, Tibet, or Taiwan? India? Turkmenistan? Turkey? Let's get real for a moment here. This whole shit show in Ukraine wouldn't have happened if the U.S. knows that there's a limitations to what it wants or wishes to do with respect to it's geopolitical aims in the world especially against proud historical hegemon like Russia and China.
Xinjiang becoming a wayward province or being absorbed by any of China’s neighboring countries invites regional war and annihilation full stop. The same goes to India with respect to Tibet and Taiwan is already a red line where China will drop the massive hammer.
Russia is recognizing the independence of two breakaway states (Donbass/Luhansk). I don't know if Russia will absorb these states?? Putin didn't say anything about absorption/annexation as far I can tell?
This fundamentally violates China's core principles of 1) "non-interference in internal affairs" and 2) "zero recognition of independence of separatist states" because it can happen to China as well. China cannot openly support Russia's actions, it's too brazen.
You are correct that nobody is going to absorb Xinjiang/Tibet/Taiwan. But the point is more about recognition of independent separatist states, we are not sure if Russia will annex these places or not. I bet Russia will just like with Crimea with some "referendum to join Russia" vote... Maybe.