You need both, the task repetition and the resting. Even better if the task repetition isn’t mindless, I don’t know why you added that qualifier.

And actually, grinding the exact same chord over and over can improve your music. You won’t become a grandiose composer, and even unlikely to become a descent musician from that alone, but you will definitely evolve from a messy play to something more comfortable over time. And likely get ideas and motivation for what to do next.

I really don’t think AI tools are good to use as a non expert, they nudge you away from meaningful engagement