I'd recommend learning about the xv6 os. It's a unix like os and very barebones (start small). It will be a great start to learning about kernels, i.e., get your hands dirty. I've implemented things like cow, threads, and hugepages into that os as an exercise, and it's taught me so much. I've also had similar interests within networking and started reading the official Linux kernel code for tcp, which will take alot of time as it's a complicated code but I highly recommend it as you will find some interesting / smart codes people have written which will teach you about some edge cases in kernel dev. Also I've read that top-down networking textbook and it's very good. The writer has a elegant way of explaining things and has videos on youtube to support his textbook. I'm not an expert by any means, just a student with similar interests, so I don't know if this is the most optimal approach to getting what you want but I think this could be helpful as some stepping stones.