The bug:

The end portal texture moves in sync with the player's first person walking animation.

How to reproduce:

Walk forwards and backwards, as well as from side to side while the camera is pointed at an end portal. The starry texture bobs up and down along with the player's view, making it look out of place.

Minecraft 2021.03.06 - 14.53.23.10_Trim_Trim.mp4