How do you design adventure games puzzles? I'm blank

I'm currently developing an Adventure Game, about a 20'ish something guy who is basically a Don Quixote but for Detective stuff, and he sees normal stuff as a big crime happening, the issue is I searched on youtube how to design puzzle and found the Puzzle Dependency Chart, and decided to try it and I just can't think of anything more than, "The guy starts in a room", and then I'm at a loss, I have a general direction of the story already but I can't plug puzzles into them, is like my mind blocks all attempts at that.