Socialism For All on YouTube does a ton of narrations for Marxist works, some short pamphlets and some entire books with everything in between:

https://youtube.com/@SocialismForAll

I also have ADHD and struggle with it. Although I'm lucky(?) to be autistic too, which balances out the ADHD traits at least when the autism and ADHD are working together rather than against each other.

Not to go all Russell Barkley on you but ADHD is very interest-based, so you'll probably find that you're not going to be able to just read theory or history because you've decided that you're going to. But if you follow where your interest takes you, you might find that you're much more inclined to read a book because you'll have internal motivation to read it.

That means chasing rabbit holes and going where your brain drags you to rather than choosing what you're going to read next.

Don't forget to check out audiobookbay for lots of audiobooks. The search function on that site is a kinda garbage so hit me up if you're looking for a particular audiobook and you're struggling to find it there.

Edit: You might also appreciate the podcast Actually Existing Socialism (available on your podcast app or on YouTube); the host speaks to academics mostly about their scholarship on topics so you can get a good summary of books that these academics have authored without actually having to read the books themselves.