Mint is Ubuntu/Debian based and uses their Cinnamon desktop environment.

Bazzite is Fedora based and uses KDE as the desktop environment.

The biggest difference is that Bazzite is atomic or immutable distro. The core systems are read only so it’s harder to break. It’s also harder to tinker with. You’re mostly limited to packages that are available in their package manager. You can install other stuff via layering if you really need to tinker.

I have a first gen Define XL that’s probably closing in on 15 years old. Still going strong as my primary desktop case. The only problem I’ve had is little cheap plastic connectors to attach the feet to the case broke. I know they’ve fixed the design for recent versions but I can’t justify the cost when the rest still works fine.