I think I've collected all the evidence but I'm a little confused as to what evidence to give Kevin to convince him
I don't remember the order of the evidence, you have to look at what Kevin says.
But I think the list (perhaps incomplete) is as follows: that Kasia is not loved in the theatre, that Kevin wants to leave the theatre, that he is not realised here, that there is sabotage at work (you need to examine the overturned boat on the shore), and that the sabotage was done by Kevin himself (a pickaxe hidden in a box).
I've looked at Ren'py code now and found the exact sequence:
Then you need to get past the worker on the dock guarding the boat - bring him a blanket and food with sleeping pills (Moran will offer to kill him
).
Well, something like that.
02.01.2025
I hope it helped...