Have you tried graphic novels, I'll admit it's not really my thing but I know there's some that have the same word count just broken up with illustrations. That or short stories could be your thing rather than a 500 page novel. You might find you can complete the story and get something out of it before you get bored or frustrated.

It could just be a matter of taste. It sounds like when I try a game outside of my frame of reference. For example I've just never got into RPG or fighting games. I know I'm missing out somewhat, but I just really struggle to enjoy them or know what to do. I'm the same with music but a bit less discerning.

When it comes to reading, I always struggled because I'm very easily distracted. If I'm not interested in the story my mind will wander and daydream. What got me focused was reading stories I already knew, namely Trainspotting and A Game of Thrones. Because I'd seen the films I was already somewhat invested and immersed in the characters and world.

My advice is to not sweat it. Being in the right mood affects your enjoyment of reading. If you're feeling happy and patient, give a try again then. It's not something you can just "power through" like exercise or a day at work.

Edit. If you can read all that, a genuinely good book will be a piece of piss.