I just went through this recently, and it vastly predates io_uring functionality, I don't remember even mentioning it.
It's a good place to learn socket programming using the POSIX sockets API, but that's it.
The GP asked for resources to understand low level network programming.
...relevant to io_uring. I was just clarifying that Beej's guide is not really that.
As someone who has written a fair amount of networking code in C, I'd assert that without an understanding of what's in Beej's guide, it will be nearly impossible to competently use io_uring in a networking context.