Technically what people often refer to as "Linux" should more properly be called "GNU slash Linux", or as I've taken to calling it, "GNU plus Linux", GNU being a holistic operating system with multiple kernel...

;)

GNU people would insist so. But Linus Torvalds doesn't use that name and he seems indifferent to the whole GNU thing. The kernel was actually named Linux after Linus by early users and it kind of stuck. The license came later. And the Linux Foundation, the thing that is now probably closest to "owning" Linux (aside from Linus Torvalds) just calls it the "Linux kernel". There is no actual distribution called GNU/Linux. And insisting they all should be called that is a bit weird. None of those actually refer to themselves as GNU/Linux as far as I know.

Aside from that, it's also an inaccurate label these days. Most Linux distributions come with a lot of non GNU licensed software. To the point where these distributions (or any distribution) would be unusable without all that non GNU software. For example xfree86 and its modern replacement wayland are MIT licensed. Some popular window managers are GPL of course. But some aren't.

And some distributions actually replace GNU components on purpose (for stability/memory safety reasons usually). For example libc is now sometimes replaced by a MIT licensed variant called musl. You can now compile Linux with llvm instead of gcc. People commonly use zsh instead of bash. There are rust implementations of commonly used command line tools. Etc.