Thank for your help.
I just tested with hotspots, it works very well and testers like this idea.
I think I can add a book that will allow you to see what are the objects harvested (objects that are added to the book as the players pick up), but just reveal a clue, not the complete solution.
I will only do this if, despite the hotspots, the players are still blocking for too long (but I still have a little difficulty, because it's a point and click, and not an interactive story in which you just have to click to advance)
I remember day of the tentacle or woodruff, I blocked a long time on scenes but I never wanted to have the solution not to spoil the pleasure of playing, and I still could finish the 2 games )