Hello Blackmoth!
I forgot to reply and say thank you so much for the hints. I'm embarrassed I didn't think to combine the tome with the note.
I've kept playing and over the last couple of months and eventually got one of the endings--not the best one, I'm sure. It's a really neat game, with some tough puzzles. It's so long and involved, with an interesting story and fun cinematic platformer gameplay. It must be hard for games to get discovered on Itch (it was lucky that I found it), especially years after their release.
Had you all ever thought about recording a longplay of it? I'd be curious to see all seven endings.
Appreciate you making the game and releasing it as freeware!