However, I have had much success with black metal bands that shriek (or whatever) in a foreign language. The fullness of the sound - blast beats, distorted guitars - just really does it for me for some reason. And I don't get distracted by the vocals because I don't understand e.g. Finnish (and with bands like Horna, it's probably better that way). It makes finding that flow state much easier, and I suspect it may be working as a fidget spinner does: a certain base level of constant but predictable sensory input soothes whatever it is in my brain that gets me antsy when engaging in an activity that requires a lot of energy expenditure without proportional immediate feedback. But as soon as you up the complexity of the music past a certain point, it swings all the way the other way and makes willful concentration pretty much impossible.
Yep. It's ADHD and its weirdness with the rewards system, for sure.