Donbas always has been the problem child for Ukraine, as it has a large Russian population and is highly "Russified" linguistically and culturally. People there identify themselves as Slavs rather than as Europeans.
This war can be over so quick. The world needs to stop caring about imaginary lines on the map and let people of Donbas and Crimea be what they want to be.
I do not understand Zelensky's undying obession of unifying Ukraine by force and at any cost. As far as 1994 there have been referendums about Donbas independence. Let Donetsk and Luhansk go, so the rest of the world can live in peace.