Selfhosted

Computer networking is basically a completely different field from operating systems and programming, though obviously some of the concepts are relevant. Turns out plugging these things into each other so that they can share information in a useful way is kind of difficult. A lot of very smart people have been working on it for almost 70 years, and frankly it's still a fucking mess, so don't feel bad if you feel a little lost.

Starting with the basics is the right instinct, in my opinion. Start with the OSI model:

https://jakarta.telkomuniversity.ac.id/7-osi-layer-the-building-blocks-of-networking/

https://www.geeksforgeeks.org/computer-networks/osi-model-analogy-osi-7-layers-explained/

This helps to break down the actual functioning of the network into logical steps. It's very helpful when you're trying to visualize the operation of some of the more abstract bits of the technology stack (like TCP/UDP), and when you're trying to think through what piece of it might be causing your problem in the moment (the router is on and the cables are plugged in, why is there no connection?). It's a map that can help you when you're lost. It's also a guide to how a lot of people who work on networking technology think, so it can help you understand how things are supposed to work.

Beyond that, Professor Messer is a great resource: https://www.professormesser.com/

If you feel reasonably confident with computer hardware components and various types of cable connectors, you can probably skip the A+ part and go straight into Network+. Because you're doing this as a home hobbyist (not for the actual certification), I recommend just listening to the courses like you would a podcast. Don't try to memorize or fully understand everything, just use it to get a grasp of the terminology and purpose of the various pieces.

I also recommend taking on a project to gain experience. Implenting PiHole https://pi-hole.net/ for your home network will cover routing, DHCP and DNS, plus you can do it with a Docker container.