I mean, base Debian should work out fine.

I'm fond of Linux Mint: Debian Edition for most of my computers, but run Solus on my travel laptop (recent change), though both of those might be problematic for your needs. Perhaps regular Linux Mint?

Not enough people here saying Debian. /j

Devuan or Debian is great.

Debian is rock-solid! A very low maintenance and comfy system in my opinion

Voting for debian as well. Apt upgrade never gave me any hassle when i needed to update anything in a pinch

Debian

Another vote for Debian.

Debian with some low spec DE like xfce or Debian basic DE

Debian base with Sway.

Since you're experienced, I think Debian is appropriate. Rock-solid, well-supported, and comes with a decent variety of DE options. I personally rock GNOME and have Timeshift set up for rollbacks if necessary.

Any of the openSUSE distros should be fine. They have immutable offerings in Aeon (Gnome) and Kalpa (KDE). I can't speak to them but I recently updated Tumbleweed after eighteen months and it was fine.

Pop OS works well for me.

I know a lot of people have said it here, but Debian.

NixOS, i was a long time btrfs with snapshots Arch user. But Nix is just more stable and makes my life happy knowing it will always work as a server, desktop, or on a laptop. The config file is easy to read as documentation as code. That can reproduce the setup and even use flakes and home-manager to copy all your dot-files with ease. Just modify the version number in the file to update it and all apps are independent of each other with no weird dependencies. Better rollbacks then btrfs as it uses systemd and you can save git of your configuration files. This is the future

Any mainstream distro should work I feel like. I'm not familiar with Fedora Silverblue so I can't say anything about it.

Fedora Silverblue or Kinoite, as you will reliably be able to update the system, even after half a year of not using it.

Updates are atomic, so either an update is installed successfully or no changes to your system have been done whatsoever, there is no in-between state (i. e. broken system) possible.

I haven't had an arch update go bad since 2016, other than a few things that had instant fixes on the home page/mailing list, whereas with Ubuntu I have trouble with every distro upgrade.

I like Fedora's dnf package manager though, it's similar to Pacman. It's been a while but last time I used Fedora I got annoyed by packages being out of date and went back to Arch

Got with Fedora, Fedora Kionite, Silverblue, anything. rpm ostree, and if you need other things, go with distrobox. RPM OS Tree will be standard near future, I think.

But I will stick with XFCE Spin tho

I found the GUI interface for firewalld on OpenSUSE was beneficial for travel. You set your open services and ports per zone: Public, Trusted, Home, work, etc. And when you connect to a network just move adapter to the appropriate Zone in the network dropdown settings. This way you arent a single zone and changing ports all the time.

Silverblue is cool if you want to explore an immutable base and install most apps with flatpak or in a container. If you want to install packages in a "normal" way you "overlay" them, it's the only major difference

Nothing beats a baremetal install of (whatever you like using).

I too use Arch on my desktop (on a daily basis). I think you will find MX Linux to be a great fit for your secondary device. It works like a charm on my laptop.

Xubuntu would be a nice easy one to install. Look into Arch as well. I actually run Arch just about everywhere and really like it.