To anyone wanting to learn about OS development, nothing beats MIT 6.824.

I finished the assignments in that course and that covers all the important aspects like processes, context switching, CPU modes, page tables and virtual memory and many other relevant topics like file systems, device drivers etc. And also it’s free.

From the table of contents this course gets too involved in ancillary matters like bootloaders or the Rust language itself whereas the focus of any OS development tutorial should be on core concepts like how processes are implemented, how context switching works, how paging and consequently multi level page tables (actually, in code) work etc.