Let the people decide
Figure 1. Ukraine: area controlled by Russia in red.
Nobody asked me and it has almost nothing to do with solving the Gordian Knot; but here's my proposal for redrawing the map in eastern Ukraine.
1) Putin gets to choose the pre-2014 Ukrainian territory that he thinks should be part of Mother Russia.
2) We have a referendum in which the voters in Putin's selected area choose whether or not they want be ruled by Moscow or Kiev. While the referendum is being organized, we have a ceasefire.
3) If 50% or more of the people in Putin's area vote for Moscow, all that territory becomes Russian. Otherwise all that area reverts back to Ukraine.
Assuming the US/EU are able to enforce a fair vote, a big if, Putin will have to pick an area where he is sure he will get 50% of the vote. If Putin rejects this offer outright, it will expose the weakness of his claims, and weaken his overall bargaining position. If he accepts the offer only to begin unsuccessful haggling over how the election is run, a cease fire is not the worst of all possible outcomes.
This would be my opening move if I were Zelenskyy.
They already did this over 30years ago. Even the most Russian portions of the Ukraine voted by 80% to leave Russia and join Ukraine. Over the past several hundred years the Russians have pursued a number of genocide campaigns in Ukraine. And they remember that. Many historians believe that if Hitler had gone to the Ukrainians and asked them to join up, he could have gotten them as allies against the Russians. This would have seriously altered the outcome of WWII.
Let's announce this now and give Putin plenty of time to rearrange populations (ethnic cleansing and importing of Russians). I'm sure it's already happened in the areas Russia controls. Instead how about giving control of all pre-2014 areas to Ukraine for a year or 2 and then have those elections?