My money is on Putin knowing that his war is not winnable, but not being able to save face internally by admitting as such. If he can poke the bear enough with incursions into NATO countries like the last few days though, he might be able to draw NATO into direct conflict, at which point a withdrawal/surrender can be sold as "We were attacked by the big bad NATO and had to consolidate our local defenses" rather than a defeat by what should have been an inferior force.

Basically, the end game is based on Putin being increasingly thoroughly out of the loop.

Remember that his only sources of information are his aides and Russian television. (Not completely sure if he watches western TV as well, but I very strongly guess he doesn't)

The aides get fired if they bring news contradicting what they have told earlier. And earlier everyone who brought bad news was sacked, so every aide has been lying to Putin on everything.

So, the end game Putin is striving for is that both Ukraine and the west grow so horrified of the degradation of civilians' lives in Ukraine that they force Ukraine into what is essentially a surrender.

And then the plan B... That's awesome in its beauty: The few tens of thousands of Afghan war veterans returning to USSR caused a havoc. Back then USSR had twice the population compared to the Russia of today. And also, now the amount of soldiers that will return is 700 000. Per capita that makes closer to a 50-fold difference in the scale.

While at the same time the federal coffers are empty.

The carnage in the Russia after the veterans of this war have returned will be something previously unseen even in the Russia. While the war is making Russians' lives worse, nothing compares to how they will be once their own soldiers return home. So, just pushing an inevitable defeat a day further into future means one day more life before the carnage begins.

It's like, you know you're in for a very painful and slow death. Even if you know it's going to come, every minute you can prolong its arrival is worth a fight.