Linux

Hyprland DE is the new hotness

Must try distros: Fedora, Mint, Void. But seriously, if you are using Nix to begin with, why use anything else? Nix is as good as it gets. If you really want to do a combo, I would recommend Fedora or Mint using Nix as just the package manager and not the hypervisor. All distros are basically the same nowadays.

Must try desktop environments: Xfce, Cinnamon, Gnome, KDE Plasma

TempleOS

I'm really looking forward to Plasma 6 and Cinnamon just had a pretty good release do there's a couple for you :)

My #1 distro recommendation would be Fedora Atomic (immutable Fedora variants).

It's still a bit "underground" and hasn't reached huge popularity yet, but I see its potential that it will very soon.

I have ADHD too and Fedora Atomic is a lifesaver. Why?

• You can "distrohop" anytime you want by rebasing. With that, you basically swap out the OS with something else (examples will follow), but keep your data and some settings. If you are on Fedora Workstation (Gnome) and want to have KDE, installing and removing those packages is a huge huge mess. On the OSTree variant, it's just one command, 5 minutes of waiting, and bam, you have a clean install. I do that all the time.
• Less bugs and better security by reproducibility. Every install is the same.
• Very quick rollbacks if something did go wrong. You can't brick your OS, which I did a lot before.
• Huge choice. See at universal-blue.org , it provides vanilla images with some quality of life changes, as well as custom ones, including "unsupported" DEs and spins, e.g. a gaming distro. They aren't forks per se, they are basically build scripts and maintain themselves, which is why they're always up to date and way better than Nobara for example.
• Distrobox pre-installed: you can just create an Arch container and use the AUR from it. So you don't need to run (and troubleshoot) Arch on bare metal, but can comfortably benefit from all great things Arch provides

If you are an advanced linux user then I would suggest giving a try to the following distros: arch, void, gentoo and (like you said in the post) nixOS.

The reason behind is that this distros are focused on the tinkering aspect of linux, the experience of setting up everything the way you want.

If you want to give a shot to WMs I would suggest i3, sway, dwm, dwl, river, bspwm, Qtile and hyperland (maybe focus more on the Wayland ones if you want to try the latest software).

Don't know if it is a must-try, but LXQt has come a long way. The file browser is excellent. Everything is fast and snappy and very traditional (start button, system tray, etc.). Runner up I guess.

You can run Alpine as a desktop. The Edge branch. New software, got what you need, installs and updates fast.

I'm slightly biased, but if you already know a bit of Linux and desire more control / customisation, or want to understand how a system is put together, then I highly recommend Gentoo Linux. The install process is pretty simple, and with the new binary package hosts you have the option of quickly installing precompiled packages to get a system installed or up-to-date.

The USE flags on packages, combined with portage the package manage enable an unparalleled level of configurability, the community is welcoming and respect user choice about how they want to configure / use their system, and the documentation on the wiki is top notch - I'd say better than the arch wiki in terms of quality overall.

Forget a DE, sounds like you need a WM. Definitely check out some tiling options like i3 or sway, especially since you spend so much time in the terminal.

I wouldn't recommend specific ones, but I would recomnend you try out distros with unique features. Such as an immutable one, one that is built from source, one with packages, one with snap, one with flatpack, etc.

This will help you understand and evaluate what you like.

What is your actual personal use case, all you mention is a terminal, which every distro will support, likely with many different choices as to terminal options?

LFS. At least once.

Garuda might be worth a try. I used it for a couple months and really enjoyed it, I only stopped because Nvidia drivers kept breaking.

https://gobolinux.org/

Coreboot. As low level as you probably get. Embedded secure element OS maybe

Some great newer tech distros would be Fedora Silverblue, or if you like Debian, there is VanillaOS. They are immutable distros, and they introduce a new way of using Linux. I like to pair it with distrobox, which lets you use regular Linux applications in a container.