Bhagavad Gita, Chapter 4, Verse 20

Forsaking the clinging to fruits of action, ever satisfied, depending on nothing, though engaged in action, he does not do anything.

Fully engaged on the outside, completely unattached on the inside, that combination is what's actually being described here.

This isn't about doing less, it's about the inner grip loosening while the outer effort stays exactly the same. Someone can stay genuinely busy and still not be internally caught up in any of it.