True Experience Book Add-on 1.21+

The Experience Book mod True Experience Book allows you to save experience in a small Book so that you can always return the experience to yourself at the right time. This will protect you from losing experience due to accidental deaths in Minecraft. You will always be able to use the experience when you need it, not to avoid danger, having accumulated a significant number of levels.

First, you need to use the Book to open the interface.

Next, you can save the desired amount of experience.

Then you can return it.

What to do if you died and lost the Book?
You need to activate the Book's link function, and then even after death, the Book will always remain with you.