Great comment, cleared up a lot of thing, thanks.

As some other commenters said, I’ve also been trying VanillaOS, which I do recommend you try out, but if you really like tinkering and messing with your system I recommend Debian, although if you like a rolling-like experience maybe try Debian Testing. And for a Debian alternative I would try OpenSUSE.

My understanding is that is has to have a certain level of the GNU core utilities in combination with the Kernel but yeah not really, it’s hard to define, maybe the use of a package manager? Definitely nothing to do with GUI, probably a philosophy in mind, not sure at all to be honest.