Maybe stupid question, but black page in chapter 3 is gibberish? Or it in some other language/code?
Feel free to join our Discord - there are some people who solved and might give you some hints! To be honest, I'm note even sure how I would approach it. I know the solution but I don't know the best way to go about it ^^'
I guess this is also a decent start? https://www.wikihow.com/Decipher-a-Secret-Code