Not sure if this is intentional, not implemented yet, or is a bug, but every plant-like block can be composted in a Composter, except for the Red Grass Plant. I'm not counting the Turnip item since it's technically a weapon that can be thrown.

Here's the items/blocks that can be composted:

Here's the block that can't be composted:

MC Version: 1.20.1
Forge: 47.2.0
Super Block World Mod Version: 0.0.8-1.20