You don't necessarily need an agenda to have a great meeting.
I'm pretty sure you knew that already.
I'm guessing you've attended many useful and interesting meetings that lacked an agenda. I bet that when someone tells you "No agenda, no attenda!" you feel chastened, but also a bit annoyed by this demand for what feels like busy work. Short, purposeful meetings simply don't need an agenda.
Every meeting, though, should have a clear purpose. Why does this group need to spend this time together?
Leaders around the world have a lazy habit of adding meetings to the calendar without making it clear why that meeting needs to happen. As Doodle reported in a 2019 study of over 10 million meetings: