Must admit both these plant suggestions look similar to each other.
Bacopa caroliniana or perhaps moneywort.
Rotala rotundufolia has more pointed leave and usually turns red leaves later if lights and nutrient is suitable.
I immediately thought bacopa as well when I first saw that picture but it’s harder to tell plants are when they are out of the aquarium water column for me.
Would suggest you google both these plant types and see which is the closest resemblance but makes little difference if you like the plant anyway and both have the same requirements for nutrients and planting care.