For me biographies are easier, like The Man Who Loved Only Numbers.

Sometimes I make Anki flash cards for interesting facts, it can serve as a motivational factor for continuing on.

I feel non-fiction books are supposed to engaged with; I am supposed to stop for a minute and stare into space turning an idea over in my head, maybe ask or email someone about it or research it online.

I think people who tear through non-fiction books like fiction often have a self-cultivated structure to when and how they read books. They pick a book or topic they're curious about and make sure they apply themselves to it systematically...

1. You'll be much more motivated when the topic is directly applicable to your current struggles, so read books on those topics.

2. You may not know what type of book structure you enjoy reading. Try reading a lot of different books and think about what seems to be easier for you. Then find more of those.

Life is way crazier than any fiction.

The tricky part is to find which style / author fits you.

Pick up a few classics, read 50 pages or so and if you like it continue otherwise stop and start the next book. After a while you'll have an idea of what interests you.