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 tell me where you live, I’ll break into your house and steal half your stuff.
Instead of fighting back or calling the police, we can negotiate so I can have half your stuff. Sound good?
You think Ukraine should make concessions with the country that invaded them?
I doubt Ukraine will demand anything less than Russia pulling out of previous held lands. Russia will doubtless demand all lands it currently occupies (and maybe even ones it claims but does not occupy). Russia’s demand could be cast as peace, though really it involves giving a massive portion of Ukraine to Russia. And if you’re thinking that might be temporary… well, just ask Finland, which lost 9% of its territory to a peace agreement in the Winter War after the Soviet Union invaded them.
Probably the same way that’s been done for centuries? Armistice, followed by a peace treaty?
Who the fuck would trust Russia in an armistice. They neg on deal after deal. Hell, they promised not to invade Ukraine if they gave up their nukes. Look how well they stuck to that one.