In this war strategic victory is not the destruction of the state, but the control over development trajectory of the rival for the foreseeable future. Russian objective is and was not to annex entire Ukraine, but to ensure that it does not become menacing part of NATO infrastructure (they are surprisingly content with Ukraine joining EU). This is political goal and thus can be pursued through hybrid warfare, which includes psychological pressure on Ukrainian population, to ensure that current administration will loose political support and will be pressured into a peace deal on terms favorable for Russia. Ukraine does the same to achieve the opposite goal, but of course with much less success.

The whole story with territorial question is part of this: possible peace settlement could include just splitting Donbas region on the current front line, so that Putin could claim victory and Ukraine could just say they did what they could. But Russia wants more, they need Donbas in original borders, which is unacceptable to Ukraine. Why? Because if this question will be settled in the peace deal, it may open Ukraine eventually path to NATO. They want to create permanent tension the same way as it happened to Georgia, deferring the final settlement by a hundred years (see Taiwan as an example, which occupies China for decades).

>In this war strategic victory is not the destruction of the state, but the control over development trajectory of the rival for the foreseeable future.

No, it wouldn't be victory, it would be compromise. And the Ukraine isn't Russia's rival, it's just cannon fodder for the West.

>they are surprisingly content with Ukraine joining EU

Kremlin says that. Doesn't have to be true.

>which is unacceptable to Ukraine

Why is it unacceptable to the Ukraine?

I see why it's unacceptable for current regime in Kiev because they can't just say "we actually don't need Donbass, never mind hundreds of thousands lives we wasted defending it".