Linux

Most Linux distros are more alike than different. They'll use different package managers, have different sets of software available, have different default settings for some stuff, but at the end of the day, Linux is Linux. Once you know enough, the distro is almost meaningless in terms of what you're capable of. You can do almost anything on any distro with the right knowledge and a bit of effort. It mostly becomes about the effort at that point.

Skills you learn on one will be 98% transferrable to another. That's why everybody says to just get Red Hat certifications; not because Red Hat has a monopoly, but because their certification process is fantastic, respected and accepted almost anywhere regardless of what they actually run. As you've seen, almost every answer you got was completely different on what they actually run in production.

The only standout differences are the newish trend of immutable distros (openSUSE ALP/Aeon, Fedora Kinoite/Silver blue, etc) and NixOS, which is also immutable but its own beast entirely. These have some new considerations separate from the rest, especially NixOS. But they're still relatively fresh on the scene, so there's no rush to learn about them just yet.