Has Putin actually called for negotiations? An off-hand comment in a Tucker Carlson interview doesn't seem quite like a serious offer.

Also it seems like Ukraine and ukrainians are still pretty much supporting war against Russian aggression: https://news.gallup.com/poll/512258/ukrainians-stand-behind-war-effort-despite-fatigue.aspx

There's no negotiation needed. Russia moving out of Ukraine and paying for all damage until everything is pre crimea. If that is all done, rebuild and paid for, then, they can negotiate for less punishment on top. That's the kind of negotiation you start because both sides have something to gain and not one to keep his unjustified war territory.