Russia is not seriously interested in finding terms to end this war. They are dictating terms to enable them to consolidate their gains, get more territory, and be better positioned to invade Ukraine again later. Pushing Ukraine to capitulate to Russia’s demands now would just be mind bogglingly stupid.
Putin should be desperate. He fucked up, and every month the war dragged on made pulling out harder. He has a choice between finding war termination conditions that everyone can agree to (and his people won’t hate too much) or letting this continue to grind his country even further into the shitter. Nukes and other WMD threats are not serious. His people, more specifically his ethnic Russian support base, aren’t willing to risk all dying for Ukraine. If they were; they’d have been dropping tactical nukes a long time ago.