Speak plainly. Putin's attacking the whole of Ukraine, not just playing games in the proxy wars he's been running since 2014. He has said that Ukraine is more or less a fake country, an accident of the Soviet system, without a real history independent of Russia, and that it is currently run by a nazi regime that he will denazify. Mind you, all of that is BATSHIT INSANE, completely ahistorical, and the leader of this "nazi regime" is of Jewish ancestry who lost family members to the Holocaust.
If Putin is not a gibbering lunatic who believes the garbage that comes out of his mouth and his regime has been flooding the zone with, then he is playing the old game of conquest and longing for a lost empire of the past. And in that sense, how is he going to win this in the long term, what's the gain? Is he going to occupy a hostile Ukraine indefinitely to rebuild his empire? Is he just going to blow the place up and retreat back to the east and Crimea? Maybe he can conquer Ukraine in the coming months, but what can he actually hold in the long term, and what will he try? And how does he do that without bleeding himself dry to get anything more than he already had before all this? Who will support him beyond those who are already his puppets (see Belarus), and maybe some other revanchists like China? China will be the senior partner in that relationship, and they will extract maximum gain at Russia's expense, as they plainly have no interest in rebuilding the Russian empire, only their own.
The only hope I can see Putin having is Ukraine folding without much of a fight, then he gets to dictate some terms. But trying to rebuild the empire, which really seems to be his intent, seems like a giant pipe dream, and doomed to fail sooner or later. Maybe if Putin had a stooge like Trump in there to blow up NATO before Russia went in he could have gotten quite a bit for himself without having to have a real, brutal war, but that's not the case.
I'll stand by what I said earlier, you'd have to be nuts to think this is in Russia's interests, it's an act that reeks more of desperation than strength. Any gain that isn't fleeting will have to be paid for dearly in blood and treasure.