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.
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.
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.
