How does Ukraine start negotiating with a country that has invaded theirs?
The same way anyone starts negotiating with anyone: open a dialogue and exchange demands, and then work to make concessions and compromises. They won’t do that, though, because then the infinite money spigot from the US will shut off because America doesn’t want this war to ever end.
You think Ukraine should make concessions with the country that invaded them?

For the sake of peace, yes, I think they should be willing to make concessions. That’s how negotiations work.

If you refuse to offer anything you aren’t really negotiating. You’re just issuing demands with no exchange.

If someone came into your country and started to rape, kill and kidnap your people would you roll over and give them whatever they wanted to stop doing that?

If the alternative was that they would rape, kill, and kidnap my people for the next 20 years without end?

I’m not willing to fight this war to the last Ukrainian.

You are Ukrainian then? Because I think they are the only ones who get to make that call.
The conflict is not occurring in a vacuum. They can pretend that they are the only ones who can make that decision, but without the West sending ridiculous amounts of money in arms and support, they wouldn’t be in a position to make any decision. As long as they’re entirely dependent on others, they can’t monopolize the decision making here.

See you have an issue in that argument. Without support (as that is what I assume would be the threat here) Ukraine has very clearly stated that it would fight on. You seem to forget that the west just lost a war in Afghanistan, who had no real foreign support.

All that cutting support off would do would drag this conflict out and make it mostly partisan action.

Whose money are they sending over?