After using a custom book editor, who was working for 1.20.2, the book turned corrupted in 1.20.4. See the attachments for the difference.

The formatted picture with underlined text and colored text is from 1.20.2
The text without colors and some nonsense is from 1.20.4

The same command is used. By converting an old world with book in a lectern (1.20.2) to the newest version (1.20.4) the same thing happens, the book in the lectern turns corrupted.

How to reproduce:

1. Go to [this book generator|http://example.com] (link: https://minecraft.tools/en/book.php)
2. Make a book with some formatted text.
3. Give the command in a command block in 1.20.2 and execute it. Place a lectern in the world with the book, if you want to check it in the new version.
   No problem: the text is identic to the preview on the website.
4. Convert the world to the newest version (1.20.4) or make a command block with the same command as before in a 1.20.4 world. Execute and you will find a corrupted version of the book.