https://linuxcommand.org/lc3_learning_the_shell.php
One of the more interesting things for me was learning how in depth some of the commands are. For example I wanted to use wget to back up a website that was having issues at the time. I built an advanced command after going through every option and learning what it did.
I repair stuff as a hobby and I'd been lucky and didn't really encounter the widespread bad cap issue. That is until I started messing with early 2000's receivers. Those are the only ones you can get cheap these days and man what a pain those are both and the sheer volume of parts that need to be replaced and in their designs.