Maxroll's Skill Planner has previews of some Legendary Class Mods

Take them with a grain of salt, I'm hoping they're confirmed to be in game but don't know for sure, but now that they've added equipment to their character builder, you can see some of the effects of Legendary Class mods

It doesn't seem to be exhaustive (Amon only has 4 listed compared to others who have way more), but enjoy browsing.

https://maxroll.gg/borderlands-4/planner