Is there a report button for players who stall the game or don't move then wait for you to leave

Lately I have faced many such players. In chess.com they can be easily reported and action is taken almost immediately against them. Is there a way to do it here during the match without leaving

No sorry this is not a feature that I have seen but if you want to suggest it you could definitely ask for it in the feedback column it has been useful for me before.

You can easily report everyone you want. Go to their profile and click the warning symbol (triangle with an exclamation mark in it)
Plus, the behaviour you mentioned will be discovered automatically by lichess and punished in case a player does it too frequently.

In additin it being detected automatically except if they actually return you just read news on other tab and just climse the tab whrere games is. Tab will 'blink' in requesting your attention.

If you want to report the player at the time of the game , you can open a second tab for lichess and report while you'll get the move sound if the player moves a piece . At mobile you can split screen and open lichess in some other browser and report the player.

@Daksh2005 don't you think this is too much of a hassle ?
I think they should add a report button on the play screen like in chess.com

Too much of a hassle? In firefox, I can do a middle click on my opponent's username, and his profile is opened in a new tab. So this is exactly one mouse click more than on chess.com. Probably most browsers have similar features.