Yellow dot next to control panel? (in menu bar)

Monterey 12.4. In the upper right corner of my screen, there's a yellow dot next to the control panel (or whatever it's called) in the menu bar. See my screenshot below. What does that yellow dot mean?

I'm having trouble with notifications; many notifications never pop up in the upper right corner of the screen, but some do. I can't figure out why. When a message comes into Messages, for example, I *never* see or hear it, however, it's enabled in Notifications. I figured I must have accidentally enabled Do Not Disturb or something, but, as you can see, I haven't: