I think that it relates to bargaining power. Right nowthe only leverage that the Ukrainians have to negotiate against giving up territory is to trade Kursk back.
If a negotiation is forced by the new US government, the Russians want that leverage gone first, so that they can negotiate to keep held territory.
Modern NATO weapons and which ammunition? Which NATO tactics without air superiority? Ukraine doesn't even get enough bullets to fire, let alone rotate troops to relieve physical exhaustion.