Does the "calm tech" movement have much to say? I feel like a theory of learning for software is more important. Of course it should be done in a pleasant way but I wasn't able to get much actionable insight out of calm tech writings.

First, there are parallels to some Software Design heuristics. The focus on simplicity, complexity hiding, graceful error handling, generalizing and reducing the surface of interfaces etc. come to mind.

So the way you structure and write your code has very much to do with wanting to reduce the mental taxation of the reader (you included).

In the UI, UX and HCI world the concept has obviously a lot to say as well.