A great deal, I'd ~~imagine.~~ I can conceptualize.
I have Total Aphantasia, and zero sense memory at all. I do have an "inner monologue" of sorts. I can't "hear" it in my head, but I understand all the same. I don't know how to explain with words and I don't know how I work either, really. My outer and inner voice are the same thing to me and I have full control over it., often transitioning back and forth when I'm alone. As in, no racing thoughts. One of the ideas behind meditation where you try to silence your mind? I don't have to try. It's not something that takes effort for me. I bring this up because this is how I'm reading books, with that silent inner voice. One of my friends is like me with Total Aphantasia, but he has no inner monologue either. Which is bonkers to me. I don't get it, neither does he! Haha. Many different kinds of human minds out there, it's not so simple.
Hard to miss what I've never experienced, I still enjoy thinking about these fictional worlds even if I can't conjure up a representation of what is written in my mind.
I read every genre. It's actually specific writing styles I lean towards. If the author is really detailed with describing environment constantly, I appreciate that. I can't really "fill in the blanks" so to speak. I also really like it heavy on the internal monologue side of things with main characters. I think that's why I liked Ender's Game so much when I was a kid.
I do prefer any visual media. I save all my book and research reading for when I'm at work these days, which is a lot of time actually. One of them hurry up and wait jobs. Books are far better when it comes to potentially constant interruptions.