I’d say i learned the most by hopping and breaking things in about 100 different ways.
I’m not sure I could pinpoint one thing in particular that "every linux user should know’… I just know infinitely more than I did when I started but still just a drop in the ocean of things to learn with linux.
I guess I’d just say don’t be afraid to try things you’re not fully comfortable with, do your disto hopping then once you’ve found something you like learn about VM’s & spin up VM’s to scratch the I need to try all the new things itch that a lot of linux users tend to have.
in the end you learn even though there’s thousands of distros they are really pretty much the same thing but just do things in slightly different ways.