True Left

"How do you find it in art?"

I don't think it is possible to describe in words. It would be like trying to describe a colour in words. I can at best offer examples of otherwise dissimilar things which are of that same colour, and someone (who is not colourblind) looking at that set of things can thus understand the common property I am referring to.

"Is 'groove' a good word to describe it?"

To me groove refers more to getting into the optimal psychological state for doing art, which all serious artists try to do before/during working. But there are many possible grooves, including many anti-spiritual ones