Taking some of the recent suggestions, and crunching them, I think we get this:
Fighting stops.
Putin keeps for now some regions.
Trade some areas for Kursk occupation by ukr. Straightens a lot of lines/defensible rivers etc.
Ukr can’t join nato, because of territorial disputes(suits nato and Russia)
NATO can arm ukr, and this is what we do, steady delivery of enough kit to ward off Russian army.
Air defense upgrade , and limited offence.
Eu negotiations.
Certificate of future support maybe, if Russia gets naughty.
De mil zone for both sides, 25km each side. Light infantry only on the border.
‘Rapid’ removal of sanctions but some sort of levy paid by eu to ukr(but netted out by cheap price from Russia for 5 years).
Prisoner exchange
Cultural exchange