[listenallyall]

In another comment you wrote "stop sign is a red octagon (with a white boundary) with the word "STOP" in the center. I could draw you a plausible picture of one without issue". The fact that you knew all of that without having to actually find a stop sign and look at it, that's mental imagery. It may be a skill some people are very good at (i.e. they can remember lots of small details) and others are not, but it's not that you don't have this skill at all.

[corysama]

What I know is that people describe not having aphantasia like

“I’m sitting in a room with a dog and a TV. Then someone says ‘visualize a stop sign.’ And, so then I’m sitting in a room with a dog, a TV and a stop sign. I’m know the stop sign isn’t real. It might be fuzzy or even black & white. But, I can see it between the dog and the TV.”

Well… I know exactly what a stop sign looks like. But, there’s no stop sign in the room with me and my dog. It’s not there at all.

[satvikpendem]

No, that is more like hyperphantasia, where the visualized object is superimposed on top of one's visual reality. Seeing something in one's mind's eye is more like there is a a buffer right above my visual reality where I can imagine something inside that buffer. It is not superimposed over reality but I can focus on both the visual buffer and the imagination buffer simultaneously.