This shader pack is very old, and is no longer actively maintained. It might break in some future version of Minecraft. It has bugs, and I am not going to be fixing them. Please do not report them to me.
FAQs:
Q: What's the difference between the main edition and the modded edition?
A: Main has the most features, but doesn't work properly for some mods that use fancy rendering techniques. Modded aims to fix this issue, by using a completely different rendering pipeline, but that pipeline doesn't allow for some of the effects that main has. Use whichever edition works best for you.
Q: Things look bad when one translucent block is in front of another one. Especially water.
A: Nothing I can do about that. Sorry.
Q: Will there ever be shadows?
A: No. Drawing the shadow map requires rendering the world twice per frame instead of just once, which will roughly half your framerate. This is an unacceptable performance loss for a pack designed to be lightweight.
Q: Does Iris support this pack?
A: As of version 1.5 of Iris and V2.10.0 of QOL, yes!
Q: Are there any config options that increase framerate?
A: Yes: Fancy Clouds and Blur are the most expensive options in this pack.
Q: I see Twilight Forest in the gallery. What is that?
A: Twilight Forest is another mod, which you can download here.
Q: The twilight forest looks broken/looks like the overworld.
A: MC 1.16 broke support for modded dimensions and neither OptiFine nor Iris has fixed that yet. Iris has now fixed it, but AFAIK OptiFine still hasn't yet. The fix requires V2.11.0 of QOL.