I remember a Skyrim mod that added a notepad, so I've seen the idea before. Although I worry that most players wouldn't actually fill it in. Perhaps a better solution would be to program in the key notes: a bit like The Witcher does as you go through the story, and it adds to the notes for each character.
I also wish that BG3 had some lore explanations for things your character should already know as a person who lives in the Forgotten Realms, for players who aren't familiar with it
