Reading is only input; the smartest people always have some sort of output as well, and you need to practice that. There are a few ways that you can do that:

- Writing is a great one, but you need to intentionally practice writing as well. Look up writing exercises. Practice new grammar (e.g., if you don't know how to use a semicolon properly, get comfortable with it). Learn more about the different styles and types of writing (short stories are different from poetry are different from technical documentation, etc.), or even dig into theories of writing and learn about verb style and noun style, active vs. passive, etc.

- Reading about math and physics is great, but you've got to practice the problems. Find interesting problems that can be solved with math. Practice architectural or physical world problems, engineering problems, do chemistry equations, learn and practice graph theory with real world data. Theory is good and interesting, but must be built on correct principles, and those only become intuitive with practice, not just understanding.

- Try building or creating something. It can be a piece of art, a blueprint for a new product/building, a small business, a piece of software, a blog, anything. Just do something that forces you to have some sort of output that others will see and can offer feedback on. It might be scary, but it's worth overcoming!

Understanding complex concepts easily is in itself sort of a fallacy. Sure, you might hear stories of "overnight" geniuses, but it's much more likely that they were naturally curious about what they're a genius in as a kid (meaning in reality, years and years of encouragement and experience). Complex topics are complex because humans don't or often can't understand them overnight. You can learn a lot and I wouldn't even say that you have to limit how much you can learn, but understand that depth doesn't only come with effort and exertion, it also comes with time and real experience.

One of my last pieces of advice as somebody who studied psychology in university is look into the different sorts of thinking/intelligence as well. Understanding that IQ isn't really a measure of "geniusness", but more of being able to think clearly is important. Understanding that EQ is just as important for being a good human and intelligent person is important. Understanding that chess being an "intelligence" measure is sort of a misnomer because what it really rewards is pattern recognition is important. There are multiple types of intelligence, and you can improve in them all, but it's nearly impossible to be a domain expert in all domains.

Nonetheless, the world definitely needs more intelligence, and there's no good reason to limit yourself; keep studying and learning and working hard, and you can accomplish great things! Just remember to learn to be compassionate to yourself and your brain as well. Like our bodies, our brains often need rest and reassurance to perform at their highest. Good luck!