I agree with you regarding imagination - the problem isn't the usual definitions of imagination, but that the process of seeing images to varying degrees (from fuzzy, brief views to "full fidelity video" they can rewind at will at the other extreme) is so deeply ingrained in most people that a whole lot of our vocabulary uses visual metaphors for the entire process rather than just for the visual aspect.

E.g. when reading I tend to skim over writing that spends a lot of time describing the visual appearance of things unless the words themselves are beautiful to me, because no matter how well written the descriptions are, they don't achieve anything for me beyond the shape of the prose itself.

(I love the structure and flow of language, so there are absolutely moments I find myself reading visual descriptions because of the descriptions themselves)

When writing, I prefer to write relatively sparse prose that focuses on how things works and relates to each other, and dialogue, rather than trying to evoke imagery that I can't see for myself when reading the text back.

I have a sense of how things relate, like a graph I can follow. So in my room I know the couch is in the corner of the room by the window and there is a desk taking up the space on the other side, with a gap between.

I can’t “see” it, like a drawing or picture, I can just sense the spatial relationships.

I recently did a little fun series of photos with my daughter at a Halloween event and came up with the idea as a series of frames and what I was trying to convey.

The end result was a complete surprise to me, because I only imagined the story and spatial relationships. The photographer said it was the most creative sequence anyone did that night.

Although it’s on my fridge that I open multiple times per day, I can’t tell you what it looks like exactly, only logically. For example I have to remember the costumes we wore, I can’t see them in my head, to remember what we looked like. So visualization ability is not necessary for creativity, I believe.

Is it common for people with aphantasia to not realize it until well into adulthood?

One of my good friends has it, didn't realize it until he was married (~40 years old) and his wife "figured it out." He doesn't care for fiction - especially written fiction, but movies/TV to a lesser extent - I always wondered if that's related. Aside from that, you'd never know - he's a good photographer and excels with mechanical stuff (rebuilding/modifying vintage motorcycles in particular).

My understanding is: Each sense has an phantastic analogue for phantastics. The hyperphantastic can override their senses with their phantastic analogues. Most people have more-or-less full control(?) of their visual and auditory phantastic analogues. The aphantastic have no/very stunted analogues with limited control, or only a partial selection, but people with a visual analogue and without other senses would probably never realize, and so aphantistics can be assumed to missing at a minimum the visual analogue but very commonly have none.

The closest physical world analogy is moving in a familiar room in the darkness -- you kind of know where the corners are, and where to find the light switch, so you can move around, and tell, if asked, what's where... But there's no seeing involved.

So, when asked to imagine something, for me the process is akin to drawing a blueprint, and then mentally modeling how that contraption could work in real life, without actually building it. Imagination is certainly involved, but it may not be the kind of imagining the requester assumed.