Question Does anybody know what causes the Red gradient damage on the LCD?

I just wanted to know if this is repairable
Only repair would be panel replacement, given there is spare panel for that tablet. Cheaper and easier would be buying new tablet.

Increasing display's gamma level may remedy it a bit but it won't fix the issue. It just makes it less visible.

and what is causing the issue
What you have, looks like LCD burn.
If it really is that, further reading: https://riverdi.com/blog/lcd-burn-what-causes-it-and-how-to-prevent-it

Backlight bleed.
Isn't backlight bleed usually white (gray)? Rather than red? 🤔