The bug
If the player's value for "XpP" is much higher than is normally attainable, parts of the GUI texture atlas can be displayed on screen.
As of 1.20.2 (23w31a), seeing the effects of this requires resizing the game window. In 1.20.1 and earlier, the effects are visible without resizing, manifesting as a duplicated XP bar. I believe this issue goes back to around the time when XP was implemented - attached are screenshots taken as far back as 1.0.0.
How to reproduce
Download the attached world file
Load it up
Resize your window to be short and wide
Expected results
On the far right of the screen, a conglomeration of UI element textures would not be visible.
Actual results
They are.
Linked issues
Attachments
Comments 2

I've been able to get this result by upgrading worlds from old versions without using editors.
Yeah... this requires third party programs to set up, you cannot do this without modifying player NBT.