I see that this feature isn't ported on forge/neoforge but it seems someone else has this feature (of course they don't have it for 1.20.1 -_-) but hopefully this would make it easier to port especially because it's mit license as well so yea

https://www.curseforge.com/minecraft/mc-mods/end-portal-parallax

The shader you linked has an issues on some versions that i'm not up to fixing and i really don't want to use diffrent backends for this feature in particular