While I can't speak to the mental health mentioned in this post, I used to read all the time, but by the time high school years hit that dwindled and I could barely read a chapter without wanting to do something else. I think that social media really took a toll on my attention span (though I can't prove that).

What helped me was making a book club with some friends of mine! When I had a deadline in place where if I didn't finish chapters at a set time (otherwise I wouldn't be able to properly have a conversation about it with them) that really helped motivate me. This also had the added benefit of exposing me to books I wouldn't normally read (this is how I was introduced to House of Leaves). I still don't dive deep into a book as easily as I used to, but it has been improving and like anything else just generally comes with practice.