Current situation is that Russia has occupied parts of Ukraine that it liked.
Zelenskyy expectation -> Russia should leave all occupied lands, say sorry and go back.
Putin's response -> I am not moving back,. what are you going to do.
Europe response -> we will give more money and munitions to Ukraine so that they can fight for more years
Putin's response -> sure, go for it.
At this point there is nothing Ukraine or Europe can do to make Putin go back.
Putin basically called their bluff and said 'Or what?'
and they have no answer.
What is Ukraine and Europe gonna do if Putin stays put?
Even if Europe puts boots on ground, it's not winning this war against Putin.
Realistically there is no way for anyone in the world to make Putin go back and that includes US.
People forget that parts of these occupied lands are ethnic Russians with loyalty to Russia. This is not a scenario where the locals are resisting Russian occupation.
When you accept the fact that there is no way you can forcibly remove Russians from Ukraine, everything else falls into picture.
Zelenskyy can either negotiate now or lose millions more and more land and then come to negotiations.