After many, many years of being asked to visualize things and never being able to do it, and not forming pictures of characters or places in my head as I read, and never being able to accurately guess what a place actually looks like based on floor plans, I have reached the conclusion that I don't have a minds eye. (I reached the conclusion a while ago, so this isn't new, but it's relevant to the slightly unusual way I interact with representation in fiction.)
In fact, not only do I not come up with a mental image of a character as I read, but I also don't really remember the details of how a character is described as looking. (For similar reasons, I don't pay much attention to those details while I'm writing, which I'm working on because I know representation matters to people in all the ways they can interact with the information, and if I don't provide descriptions that show otherwise, people are going to assume all my characters are cisgender heterosexual able white people.)
One example I like to use for this is Hermione. The book descriptions of Hermione could be describing me, and I didn't realize this. After I saw the first movie, with Emma Watson as Hermione, while they were still trying to give her actual frizzy hair, I picked up on the bit where Hermione is a character who looks like me, but that didn't make Emma's Hermione take over the non-existent slot for my mental picture of Hermione. It didn't make me take over the non-existent slot either, because that slot doesn't exist. (Also, the book version of Hermione and I are fairly similar, personality-wise, which is the way that I can understand and interact with.)
For me, the non-existence of mental images for characters means that I personally don't much care what a character looks like. I care about it for the people who'll notice and care because they have minds eyes like that, and I care about it some (still not much) in movies because the pictures are given to me, but as far as making me feel represented goes, it really doesn't matter what the character looks like. I need characters who act like me, whether or not they look anything like me.
Give me characters who are awkward even when it isn't cute. Give me characters who avoid shopping because it's loud and bright. Give me characters whose interests don't line up with the idea of "geek" or "jock" or "creative type" or any of those, but have a mix from all. Give me characters who are good, really good, at some of the things they like but have to work hard to even manage "not terrible" for some of the others. Give me characters who act like me, with personalities like mine.
The physical descriptions matter for the people who can translate those to images, but that's not me and it will probably never be me.