How do I learn CS fundamentals beyond web development?

Use a roadmap as a map, not a checklist you have to finish before making anything. Pick one programming language and get comfortable writing small programs, using a debugger, and explaining what your code does.

Then work through a structured algorithms course, including data structures and complexity. The Princeton Algorithms course is one option. For systems topics, pick one subject at a time rather than trying to study operating systems, networking, and databases all at once. Operating System Concepts and Computer Networking: A Top-Down Approach are books to consider when you get to those areas.

A routine could be a few study sessions on the course material, followed by exercises and a small program that uses the ideas. You can revisit older topics when you notice a gap. You do not need to memorize every detail forever.

Start the mobile app now. Waiting until you have covered all of CS is a pretty good way to postpone the thing you actually want to do.

Build something small in React Native and connect your study to problems you encounter. A data structure can help organize app data. Networking becomes less abstract when your app needs to fetch something. You can still use a course for depth, just do not make finishing the roadmap a prerequisite for starting.

Discrete math is worth making room for early. Boolean logic, number bases, sets, and counting come up in different parts of CS, and studying them deliberately can make later material easier to follow.

That said, it does not have to be a long detour away from programming. Work through problems, write little programs that demonstrate the concepts, and move between the two when one gives context to the other.

Whatever resource you pick, do more than watch it. Type and run the examples, change them, predict what will happen, and debug the surprises. Then try an exercise without looking at the solution.

If an old topic has faded, revisiting selected coursework or exercises is reasonable. Repeating an entire course is not the only option, though. A small project can show you which pieces you actually need to review.

For the language issue, a structured Arabic course that you can follow consistently is a reasonable starting point. Compare its syllabus and exercises with the topics you want to learn, and use English resources when you are comfortable enough to fill gaps.

Try sticking with one main resource for a topic rather than collecting a dozen. You can look up unfamiliar English terms as they come up instead of waiting until your English feels perfect.