Did you just, not read the OP and come straight to this person's comment to argue with them based off the least charitable interpretation? The OP already uses Linux Mint Debian Edition. This person mentioned "flavours" of Linux, clearly meaning the various 𝑥-based families of distros (ie Debian, Fedora, Arch etc). Which is pretty solid advice when it comes to learning the CLI in my opinion. I think they were trying to gently nudge OP away from their second EndeavourOS install, as even though ArchWiki is great (sorry KDE but it has better Plasma docs), OP would end up pretty lost on trying to use those skills back on LMDE.

But to circle back around, Debian, the distro, actually is a good choice for learning the CLI because it can be installed without a desktop environment, potentially using something like Distrobox. That way OP could learn the CLI within their LMDE installation in a sandbox, so they don't risk messing up their main computer.