What is a special interest exactly?

I'm currently being tested for autism and ADHD and this is one of the things I struggle to understand.

I have loads of interests and they take over my life again and again but I don't think I have anything much to show for it. No cool collection of rocks that I can name every mineral out of. I love true crime but I can't retain information very well, I never remember dates or names, all I really do is listen to podcasts again and again or watch documentaries.

I love Elizabeth the first and even drew a few pictures of her time to time, but again I don't feel like this is at a crazy level of interest.

I think I forgot me I just like stories, since I was little I wanted to be a writer and everything in my life has revolved around stuff like that. Like I've considered film or game making and it's all about being able to make stories. But I don't think this counts as a special interest?

Like to my understanding a special interest is when you learn pretty much everything you can about a thing or subject to an abnormal level because it's your obsession. Least this is what Google told me, it also said it's extremely uncommon for autistic to not have a special interest.

The thing is there's stuff I would love to be super knowledgeable about. And maybe I would if I could retain that information but I can't, I just end up listening to the same stuff over and over again.

There's a book series I am obsessed with, I've been listening to it non stop for years now, it's got about 15 books out now and I usually listen to the entire thing 3-4 times before having a short break to take interest in something else. But I still can't quote it well or anything. Like you'd think I'd at least be able to nail the opening paragraph or something but I'm too dumb. I even bought the books, the manga and the spin offs because I love it so much but it just doesn't meet that level of a special interest, right?

Like, with true crime I bring it up all the time. I don't think a day has gone by since I was little that I didn't talk about murder or something. I'll tell people all about different cases but again I can't remember names or numbers, whenever I think of a number it's always "7", it's so hard to remember the actual numbers.

What's your opinion on this? I really want to know the opinions of diagnosed people if possible.