I didn't know UCB had such good courses available entirely for free, including videos.

Do you have any course suggestions for studying Operating Systems, Databases, and Computer Networking?

Also, I wanted to ask if it's worth self-studying the entire (most of it) CS undergraduate curriculum or if it makes more sense to invest in learning development tools and frameworks, get a job ASAP, and learn this theory on the go.

OS: https://pages.cs.wisc.edu/~remzi/OSTEP/

Databases: https://15445.courses.cs.cmu.edu/fall2022/ | https://15721.courses.cs.cmu.edu/spring2023/

Computer Networking: No idea

No it's not worth it, learn the basics and go write code and build stuff.

Curious, but what do you find the most difficult or confusing so far in your journey?

Math :)