Watched a video uploaded 2 days ago showing this option and what it could do, but it isn't there and I couldn't find any obvious commits that mentioned it being removed (downloaded the dev shader today)

Tested on a 1.20.4 Fabric instance with the bare minimums + DH (screenshots are from an instance with a ton of mods so I tested with the list below and found that the option is still completely missing.)

Distant Horizons 2.1.0-a
Fabric API 0.97.1
Indium 1.0.31
Iris Shaders 1.7.0
Sodium 0.5.8

..I just looked at a suggestion and found the explanation, probably shouldn't have had to look there to learn that it was intentionally disabled.