It's not about the line changing
Russia isn't fighting Ukraine, it's fighting a multi state alliance who are providing hundreds of billions and a weapons supply from across the world
The Ukrainians are now trying to recruit young men to fight, after that they will have nothing left
It may take the Russians 2 years to move 10 meters, but once the Ukrainian front line collapsed the Russians will surge forward
Russia has ALREADY taken a brunt of the most important mineral deposits and wants to push for the rest, what the USA wants is a deal which leaves the remaining minerals for the U.S to take and wants the Ukrainians to willingly sign a deal giving the U.S access to them whilst the Russians keep what the have taken
The west is looking like a joke at the moment to be honest
First of all, you do know that this line
"It's not about the line changing"
and this line
"but once the Ukrainian front line collapsed the Russians will surge forward"
Is contradiction in term, right? I don't know how much you know about fighting a war, but you need to change the front line in order to collapse it. The line is not going to collapse itself. You either need to probe or breakthrough the line in order for them to do it, which mean the line has not move at all, means they didn't have any breakthrough, unless the Russian is doing nothing on the frontline now, which we know is not true, then it mean a very bad situation for Russia.
On the other hand, I still don't know why anyone would think Ukraine has running out of people, first of all, you do know there still weren't any general mobilisation in Ukraine, right? Ukraine is a big country, not like Estonia or Lativa. It have 45 million people (well, 40 now give or take) so let's say if Ukraine started general mobilisation and take 1/10 of the people and put them in uniform, that's 4 million troop there, that will take a long time for Russia to chew thru, again, would I say Russia have manpower superiority? Sure, but for that to show and degrade their enemy capacity, it will take multiple decade, because Ukraine aren't small either. You are talking about 150 million vs 40 million.
And finally, as I said, for the progress Russian made, they can't even dictate the lunch menu on the negotiation table, look at it this way, Russia is making 10-15km gain a month, in Donbas, virtually nothing in Kherson and Zapo (getting lazy) and Kharkiv so in what way would I relent my request on the negotiation if I am Zelenskyy? I can wait, it's going to take Russia more than 4 years to take the entire Donbas, so why would I not wait until Trump is gone, and a Ukraine friendly US to hold talk? I mean what are Russian going to do anyway? Roll back on the territories they want to keep if we have a talk now? Because that's what Russia is going to ask for, the control of the 4 provinces in exchange of a ceasefire, I mean it's not going to be Zelenskyy resign and collapse the government or having Russia control anything other than that 4 provinces, so again, if I am Zelenskyy, what have I got to lose if they are going to ask for those province anyway? If it was me, I will keep fighting, again, the Russian aren't going to roll the entire Donbas in 4 years, then why would I talk now? Unless you are able to force my hand.