You're welcome
Plants like Java Moss, Anubias, and Java Fern basically require no maintenance (except, of course, trimming off decaying leaves, as with any plant). They are simply tied to aquarium decor, and that's it. And they're healthier for your tank than fake plants. But, of course, it's all up to you

Anyway, I don't think one small Anubia would hurt

And Java Moss can look beautiful in such a small tank, serving as a "carpeting" plant. Just weigh it down on the gravel and it will grow and spread over the floor. I am sure your fish would like that.
But like I said, I totally understand if you don't want live plants. Another good thing about these undemading plants is that if they start doing poorly, you can remove them from your tank anytime, without a problem - since they don't root in gravel.