Here’s a couple of examples Keep talking and nobody explodes — The most popular in the list I think
Uncle Chop’s rocket shop — the game where you are repairing your client’s rockets by following the in-game guidebook
Tin can — here you are also repairing the spaceshp but this time you are it’s capitan and you are in space in the middle of nowhere
I love Zachtronics games that have been recommended a few times already. But for a different genre…
Ni no kuni is a RPG that was kind of that, with a big (originally physical) book of magic. But since it’s been remade on many platforms as a digital download, the book is there in a rather boring (but useable) pdf reader-like UI and has been made a bit less useful.
It’s still rather charming having this in-universe codex-like book listing gameplay elements, items, recipes, bestiary, and bits of lore about the world (and some pages just telling random fables about whatever). Nowhere near required reading for the game though, just occasionally useful.