It's difficult for Russia to do that today to be honest..China has grown bigger and more powerful, so Russia can't do that to them anymore unlike in the past where they took so much territory from China(territory almost the size of Europe was lost by China due to Russia) and they would have taken even more if not for some other geo political events by other western powers and Japan.
So it's not feasible for Russia to do so, as China has now grown up. However , the day China grows weak again anytime in future(bound to happen as no country can be on top forever,) then Russia might start having Designs on China as well.
Anyway, I don't see anything wrong here geopolitically speaking. Every country will.always try and get the best for their interests (including territory). Only difference is that Russia has just been much more brazen in it policy of expanding its territory to the detriment of its neighbours . Its more used to this policy and as such its establishment is geared towards such a policy for a long time. China by contrast is more of an isolationist introvert power and as such might not necessarily display such a policy.
Agree. Funny enough China has never recognised Russia illegal invasion and annexation of Crimea. Same with Eastern parts of Ukraine.
It's ironic but actually follows China's policy of respecting country's borders and sovereignty, something Russia doesn't recognised per se giving its history of expanding its territory as well. On this note, I will say the Chinese have been rather consistent and Russia invasion of Ukraine is no different(no support from China), China has refused to even provide ammunition to aupport Rusias war, in fact several Chinese companies even pulled out of Russia due to fear of attracting secondary US and western sanctions (which represents a far bigger market for them ). So I won't say China ever supported Russias invasion of Ukraine, if anything they have been constantly mentioning that Ukraine's territorial intergrity should be respected, while recognising Russia security concerns.