Honestly, it depends on what you’re trying to do with your machines. If you are looking for a stable desktop environment, you don’t need to dive that deep. (At least, to start.) Just install the defaults, and read a basic tutorial on using the Bash shell. (Even if you move away from bash, lots of scripts and such use it by default, so a passing familiarity is highly recommended.) Especially learn about installing programs with the package manager. (‘apt-get’ for Mint and other Debian-based distros.) The defaults are gonna be generally sane, especially in Mint. If you want to get into deeper waters from there, you’ll have a stable base to start from.
But. If you want to configure your machine, top to bottom and really understand how Linux works… Install Arch. Not even joking. Arch installation docs are very detailed and walk you through setting up every part of your Linux system. Be prepared for your first time to take a few days to complete. It’s a lot to take in. Start with a computer you can leave offline for awhile.
I learned a ton by installing Arch. And then I went back to Debian-based distros because there was less active maintenance. (Note that this was over a decade ago, so things may be better now. YMMV). This is definitely Learning The Hard Way, but it’s honestly the most effective thing I can think of.
Linux is insanely customizable. You can swap out and/or customize pretty much every aspect of it. It can be overwhelming. I recommend taking things on a bit at a time, but I’ve rarely used software that’s as easy to find free support for.