I'm an amateur historian so don't take me at my word. But if I'm Zelensky, I would throw everything I have in my armies for an offensive to seize Crimea. I agree that retaking the Donbas is out of the picture but that's not really necessary. If Putin loses Crimea, there's no way he will be able to spin his way out of that one. Unless he decides to nuke the Ukies to save his @$$.
Has any historical offensive effort ever retaken Crimea?
(I’m thinking no…)
Even if by some miracle Zelenski was able to dislodge Putin from Crimea, there's nothing preventing him from returning. Maybe not next year or the following, but Putin isn't going to give up on Crimea, or the Donbas land bridge connecting it. He'll regroup, replenish, and return again.
The only way to prevent this would be a NATO "peacekeeping" force in the region, and such a force would be viewed by the local populace as a hostile foreign occupation and treated as such.