What's the best way to study/learn math/science in a more thought provoking problem solving way rather than just memorizing problems? Actually, same thing with reading too - how do you not read like a pleb sounding out everything in your head?

Maybe I'm not asking the right questions either. A little background is that I've been wagecucking for around 8 years now and I let my brain completely go to waste while doing it. I'm finally unemployed and using the time to better myself. I'm not studying for a degree or anything, but I just want to be better at problem solving/thinking and using my brain in general. I don't wanna be a braindead wagie again. I heard that not using your head too can cause memory issues down the line. It would be fun to work myself up to higher level math, reading, writing, problem solving, etc. just for the sake of me. At the very least before when I was younger I remember being able to sit and think about something and figure it out. Now I just blankly stare at things.