What I've noticed, as mentioned by others before, linesmen delay a looooot time to react, or they just don't react at all.
I remember a header goal in group stage, cancelled by VAR as offside, France IIRC, the referee made sign with his hands, while the linesman, although was following the offside line, did not wave his flag.
It was so strange, cause referee was in straight line behind, it is impossible he could spot any offside, if the linesman couldn't.
And another question of mine, if linesman stays still, who calls the referee about the doubt, to check to VAR!! The 4th referee? The VAR control directorly? Like it happens with the commissioners in Basketball?
What I understand is, either UEFA gave them (linesmen) the direction, if they have doubts, to not take any action, or they just rest assured that VAR will find the truth either way, so they prefer to not take any decision.
I mean if you are a linesman and you flag offside, but VAR proves it was clear goal, you take a little psychological piss at the moment.
But if a controversial goal is scored, you just don't do anything, VAR canceles it and everyone is happy.
It is like the old saying, when you don't do completely anything, only then you are flawless, cause you can't make mistakes.