Linux

"I take full responsibility for my Arch system."

For getting better at terminal I would suggest looking into alternative shells. Bash is fine, but it’s not exactly user friendly by default. Something with more robust auto completion like zsh or saner defaults like fish could make the learning experience easier. You can always come back to bash later.

For understanding how the OS works I would start by reading about the file system layout, then look into the init process.

I got to the point I am at through a series of projects of increasing complexity. First I ran a web server on my machine to copy files over the network. Then I used a spare PC to make a simple SMB server. Later I made it into a HTPC pirate box, for streaming stuff downloaded off Usenet to my Xbox. At some point I ran a minecraft server (before docker came along and trivialized this), and got into a bunch of sysadmin and programming stuff and that’s pretty much it.

If you're in the position to take certificates then that's a another way of learning a lot. At least it has worked for me. I've over the last half year taken RHCSA and RHCE from RedHat - though paid by work. Theses in specific are expensive, but I'm sure there are other ones that are cheaper. This would also allow you to 'show off' your skills in an official way should you need to, for applying for certain jobs etc..

I at least find this way to be helpful as you have to motivate yourself to learn and pass an exam to get the certificate. It might not be for everyone though.

I learned a lot by using a less common distro (solus). When I would have a problem, the solutions I could find on forums or arch wiki wouldn't apply to my distro directly, and I would have to look into the solution for long enough to understand what needed to change in order for the solution to work.

You can probably do this on any distro, just by not using commands you find online until you understand what they're doing and why that might fix your problem. Arch wiki is a great resource for any distro, even though it won't always be accurate for the distro you're on.

Using tldr to learn commands. It gives you the information you are probably looking for in the man page but it's not buried among lines and lines and lines of arcane stuff and it's formatted in a readable way with helpful examples. Saved my sanity more than once.

I'm not saying "don't read the man pages", they are great way to get a deeper understanding of commands. But when you are just wondering what a command does and how it's commonly used, then a two lines summary + example is much more helpful than an essay going in minute details over everything.

Since it takes a lot less time than hunting the same info in the man page, you can run it before every command you are not familiar with, without too much hassle. Then if you want more info you can check the man page.