Basically, XLibre was a project that forked XOrg and tried to make it suitable for modern use. If you don't know what X11 (XOrg version 11) and Wayland are, in a nutshell X11 is an ancient display server for Linux that handled things like rendering windows. Being so old, it had lots of security issues, so the Wayland protocol was developed to replace X11.

Nowadays the majority of applications support native Wayland or XWayland, the compatibility layer for X11 apps, and both GNOME and KDE Plasma have committed to becoming Wayland-only. I believe Cinnamon (and therefore Mint) will soon switch to Wayland too.

However, there are a few people who advocate for staying on X11, perhaps they rely on a specific app that simply doesn't work with XWayland, or maybe they are just stubborn. Whatever the case is, somebody decided to create the XLibre fork, and the reason they did so was because they were booted from XOrg for promoting conspiracy theories (antivax stuff, COVID is a government conspiracy, WW2 was forced upon the Germans, that sort of insane stuff) and distasteful political opinions. XLibre broke compatibility with a lot of XOrg drivers, making it a bit of the worst of both worlds.

If you mean Artix Linux, I believe it's a version of Arch that doesn't use systemd.