You haven't given any info regarding what you want to try.
If you just want to try something different, Arch Linux is an obvious one. A nice learning experience. However, I'd say rolling release is not as recommended on a machine that you'll be using less than twice a month, since I hear people say you want to update your stuff no less frequently than once a week on a rolling release OS.
So another idea is NixOS. I think it comes with a stable release option? I haven't tried it, but it's another option if you want to install something for the learning experience.
If you want something easy to install but different, consider Fedora or OpenSUSE (either version)
For desktop environments, if you want a learning experience for something potentially fun, try a tiling window manager. Sway is one that I'm trying right now (it's just i3, but with Wayland). Or for something easy but different, any of the big DE will do, like Gnome. I haven't tried anything other than KDE or Sway.
Maybe try silverblue to see what the immutability thing is about? If you want to stick with what’s familiar, kinoite will give you KDE. If you’d rather try something different, sericea will give you sway.
Arch btw: it is much stable that many Linux users think, there are a ton of guide to do/repair things thanks to Arch Wiki, and, last but not least, it has the AUR repository in which you can find basically all software you will ever need; the only malus the AUR repository has is that you have to compile every software you install with it (even if sometimes they are precompiled).
P.S. if you want a "ready-to-go" arch distro, install EndevourOs and set the btrfs file system with timeshift. Here's a guide.
I just installed NixOS on my laptop. It is very foreign to me coming Debian then Arch. Everyone is saying NixOS is worth it so I am going to give it a solid run. I would suggest NixOS if you have time to learn and Arch if you want more familiarity
10/01 Second Morning Update:
@cocolopez@lemmy.world The machine is spare for now, eventually, I would like to turn it into kind of a modern clone of an HP85/HP87 - Good plotting, Nice BASIC. Perhaps replace BASIC with Python once I am more comfortable with Python.
I usually prefer having any side machines running something more stable than the main one, as I'm always bound to use and mantain them less often.
Good luck finding something more stable than Debian tho. Maybe something like LMDE, that just got a new version out and is looking great, or trying out an immutable distro.
Honestly, just test out a bunch of different distros over the course of a couple of weeks (or months even). As for which distros are worth considering for 'playtesting', that's entirely reliant on your personal 'Linux Journey' and whatever you find interesting. Though, if I'd be forced to make a list, then it would consist of the following:
Start off with Arch, Fedora, Linux Mint, openSUSE Tumbleweed and Ubuntu. (Debian is absent from this list because you're already using it.) You might even combine this with using different desktop environments on each; as this might have more influence on the experience than the distro itself.
After indulging with the 'veteran-distros', there are some different directions you could go from there. Perhaps you could try a distro that
doesn't use systemd; the likes of Alpine, Artix, Devuan, Gentoo, Guix and Void come to mind.
is 'immutable'; the likes of blendOS, EndlessOS, Fedora Silverblue/Kinoite/Sericea, Guix System, Nitrux, NixOS, openSUSE Aeon/Kalpa, Vanilla OS and Ubuntu Core Desktop come to mind.
takes security and/or privacy very seriously; the likes of Kicksecure, (openBSD, QubesOS (even though neither are Linux distros),) Tails and Whonix come to mind.
holds a conservative stance in regards to software and doesn't like to enforce change to its users. This enables you to learn the intricacies of its system once without ever having to forego that knowledge as times passes; Slackware.
is unrivaled in terms of freedom it allows its users; Gentoo.
unshackles itself from GNU; Chimera Linux and (to a lesser extent) Alpine comes to mind.
I have a similar machine which I wanted to run Mint on. For whatever reason I couldn't get the trackpad to work (it worked on the LiveUSB but not the install, whatever). I tried Tumbleweed and it seems pretty good.