I agree. My 1:1 invites explicitly frame them as an opportunity to point out where I'm failing in supporting your goals, things you want to accomplish and questions you have about anything from the trivial to the strategic.
I don't use a formal agenda but our 1:1's do produce explicit action items with one of us assigned and a due date
I don't use a formal agenda but our 1:1's do produce explicit action items with one of us assigned and a due date