Their little, er, biting clacker things are not strong enough to eat most plant leaves. What they can do is eat parts of the plant that are not healthy, or are decaying. This is actually helpful for the plant even though it looks like it’s not.
I find that when I feed mine algae pellets too often, they get extremely lazy about the glass and ornaments. But, I really love my snails and sometimes will feed them a pellet.
Also, Anacharis tends to get a lot of algae on those little leaves. My corys really go at it also. Unless it is stripping them off to the stalk, I would not worry.
He’s almost certainly eating what’s on the leaves. I have so many plants in my tank that my 3 nerites don’t even touch the walls of the tank, they almost exclusively prefer to eat the algae and biofilm growing on the plants
I put in algae wafers about once a week, but I've never seen him touch them.
I sometimes put in cooked zuccini, but he also doesn't touch it, and it will grow white fuzzy stuff so I don't add it that often.
I had a pretty bad algae bloom, so I turned off my tank lights for a few weeks. It killed all the algae (which was covering every surface and would bounce back in days after removing), but now I'm worried about my nerite having enough to eat.