I agree; I mentioned headless server because that would be a more “pure” and general Linux administration - learning how to administer a SUSE Linux using the graphical yast tool won’t translate as well to general Linux admin as if you learn and understand how to fo it in the command line and config files.
And absolutely; one can use Firefox, LibreOffice and any other tool on Linux, but I don’t consider that as “learning” or “knowing” Linux. My wife uses exclusively Linux for 20+ years (because when she left her job where they still had Windows 95, that’s what the desktop at home ran; kubuntu). She does text editing, internet banking, shopping, browsing, printing, everything there (even updates sw through the gui package manager), but she doesn’t “know Linux”.
You can setup a Linux system for a computer illiterate, and they may happily learn how to use it for their social media and streaming consuming, and whatever endusers do in their computers, without ever knowing that’s “Linux”.
Strictly speaking, that already happens. How many Android users know they are running on a Linux kernel?
That’s why when OP said “learn Linux”, I prioritized the admin on command line; as you don’t need to really “learn Linux” to interact with it through automated/graphical admin tools (no shame on doing it, they’re sometimes quicker and more practical than command line).
What I mean is that learning how to use cPanel or Yast is useful, but you’re learning how to administer as system through a tool, which in theory could even be adapted to administer a non-Linux system.