@patatenouille Hey, thanks for the feedback and for playing the game. I think the comments you've left are great.
Regarding the font; because I used Pico-8 I was pretty limited with what was achievable in the time limit, and just went with the default font. The resolution of the game itself is so low (128x128) that something larger wouldn't be super easy to lay out with the amount of stuff going on-screen.
The flip interaction was an interesting and tricky one; for most places I tried to make it obvious by representing anything that could flip as a stack of paper. (The intent being that you click on/near the next sheet.) The envelope, as you found, is the outlier. I wanted to add an additional affordance for this (I was considering either a different cursor or a highlighting rectangle) but unfortunately I just didn't have the time to put anything in, so I left it as-is for the submission. I will probably make an update after the voting is over and this is one of the things I want to add.
Thanks again for the feedback and for liking it enough to play to the end.