People evidently did not care about the war being UN-sanctioned or not. The rule was removed at that point, although with the structure of the UN and its security council it was perhaps inevitable that people start to ignore it.

Especially with history in mind it is quite clear that Russia would take any right that former competitors took themselves. Having lost the cold war or not is secondary it seems. Of course any argument will be used to the largest opportunistic degree. Putin may have believed that invasions now always need to be sanctioned and there was a time where it probably looked like that.

That Putin wants to rebuild past empires is something he openly espouses himself now. Although I do believe this is directed towards the domestic population. I also think Russia did believe that the US tried to topple government in Ukraine and saw a need to react.