Very impressive. Aesthetically, this game is absolutely top notch and in addition to that it's also a beautiful showcase of minimalist game design. The most important aspect of designing a jam game obviously is thinking economically, and having the gameplay systems build directly on the well realized visuals is a very elegant approach to that.
Great level design, too. Nice prop composition that further enables the photography mechanic in addition to the rendering, lush foliage, natural/tame elevation, fairly big map and despite all that super easy to navigate/keep track of where you are and what lies where - great use of landmarks and a well designed initial spawn point.
On a smaller note, I appreciate that there's a jump - many walking sims feel rather rigid and are littered with invisible walls - ironically I feel like that walking sims in particular really profit from a high degree of freedom in traversal. The jumping also works well in tandem with the accurate collisions of environment props - really adds to the immersion.
Now, if I was to be OVERLY critical, those would be my nitpicks:
Flipping through the book is very slow. A proper system using some form of input queuing would have been overkill for a jam game, but I feel like the animation itself could be played faster. The main reason the flipping anim feels slow / clunky is that (at least I would assume so) the pages turn all the way to the back of the book, but because of the perspective from which the book is viewed only the first half of the animation is actually visible - which feels like input is locked for a significant amount of time after the animation has "finished"
I would lower the near clipping planes of the camera (or maybe slightly increase the horizontal extents of the player collider?). Walking into solids regularly allows the cam to see through environment props which is probably not intended and would be very easy to fix.
Some additional sound effects would have been nice, like a page turning one for flipping through the book.
As others have already pointed out, binding quit to main (with losing progress) to tapping escape is a little dangerous :P A decent fix that's easy to implement would be binding it on hold instead of tap.
That's all :D Congrats on getting this amazing entry done in just 3 days.