If I remember correctly, it's not that the skill level needs to be high, but that the task has to be difficult enough to be challenging without being so difficult as to be daunting.

So you can still reach a flow state as a low-skill person as long as you flirt with the limits to your own skill level without getting frustrated (i.e. being highly skilled is not necessarily a prerequisite to be fully engrossed and challenged).

A bit more of a deep dive, but stuff on Daoism (esp. Zhuangzi) might be a nice complement too -- it influenced Zen (or Chan, as it was called in its original Chinese form). And not coincidentally, Mihalyi's son Mark works mainly on Daoism at UC Berkeley.

Added to the list, thanks.