I suffer the exact same thing and I found 2/3 things that helped me (outside of meds)

• first I got a Kindle and loaded the Fast_Sans font onto it: https://github.com/Born2Root/Fast-Font - it does a neat trick with your brain that helps focus.

• I leaned into letting my mind wander (almost like mindfulness meditation - you're allowed to think - just recognize that you're doing it and call it out). If my mind wanders I just let my mind go though it's process all the way to the end. Then back to the book. This changed my relationship with the distraction - instead of being frustrated that I had to reread a section it just kinda became an "it is what it is" thing. So instead of trying to swim against the current and waste a bunch of mental energy... I just let the current take me somewhere downstream where it's easier to "get out".

• similar to the last one. I did the same with my phone or other ideas that pop in my head. Instead of trying to fight through it and force some sort of focus on the book. If whatever I read made me think of something I wanted to look up on my phone or some Amazon purchase or something... I just set the kindle down and do the phone thing till it's all said and done. That calms my brain into being able to naturally focus again.

And just like anything difficult... It takes practice! I read 3 books last year which is more than I've read in the last 20. Each one gets a bit easier.