The bug
You're not able to use Ctrl+Home or Ctrl+End to jump to the beginning/end of a text while editing a book and quill, like you're able to in most text editors. Instead, it has the same effect as just pressing "Home" or "End", respectively.
This might be working as intended.
To reproduce
Get a book and quill
Write something in it that spans multiple rows
Move your cursor into the middle of the text
Press
Ctrl+Home
❌ You're just at the beginning of the line you're currently in, not the beginning of the entire text
Press
Ctrl+End
❌ You're just at the end of the line you're currently in, not at the end of the entire text
Can confirm in 20w51a.