lancalot

Options include:

• Installing them through brew; this is setup, enabled and configured correctly by default on uBlue projects like Aurora, Bazzite and Bluefin.
• Installing them within a container; be it though Toolbx or Distrobox. This is what Fedora Atomic initially intended (and probably still does).
• Some users got a lot of mileage from utilizing nix to this effect.
• If all else fails (or if you outright prefer it this way), you can always layer it through rpm-ostree.

the fact that Fedora is the only (at the least that I know of) distro that has proper SELinux implementation.

AFAIK, openSUSE Aeon(/Kalpa) does as well*.

Yup; at least to some extent.

I don't know why, but openSUSE has had difficulty garnering popularity overall (aside from Germany).

A possible explanation, which also ties in to Fedora, is how both are the open source variants to corporate distros; SEL and RHEL respectively.

Arch and Debian are more community-driven by comparison.

For Fedora specifically, people couldn't regard it as anything but a testing bed distro; especially if you see how back2back they were with adopting new technologies like PulseAudio, systemd, Wayland, GTK 3/4, PipeWire etc. To be fair, openSUSE was the first to default to Btrfs and auto-snapshotting with Snapper*. Fedora was also facing competition from industry darling CentOS; similar code base, but a lot more stable.

Thankfully, since a couple of years now, Fedora has recognized that it's not cool to expect your user base to be sadistic. And together with the (unfortunate) downfall of CentOS, Manjaro and Ubuntu - Fedora has amassed a very healthy user base. And with how quickly Bazzite is becoming the face of gaming Linux (at least until Valve releases SteamOS), I don't think it has even peaked yet.

Historically, (at least for hobbyists/enthusiasts) Fedora and openSUSE have been a lot less popular compared to Arch, Debian and their derivatives. While not necessarily representative, Boiling Steam's chart -in which ProtonDB's data is used- does indicate to this as well.

Just my 2 cents.

I had something similar going on in Fedora Silverblue. I didn't really want to fiddle with it at the moment, so I just uninstalled whatever I got from ProtonVPN and the update went smooth afterwards. I hope someone else can point you towards a better answer.

Quite the contrary, the commit log on Github looks pretty healthy.

On what did you base the following:

it has not been updated since a while.

You can still edit it. Please consider doing so 😅.

should I be looking at any other distros?

From what I can tell,

• containerization is appealing to you; almost all of them employ this to some degree, but some more than others. More on that later.
• your preference goes out to (closer to) stock experiences rather than opinionated ones

I take it that you'd rather stick to the (relatively-speaking) more popular options. Not that popularity is necessarily good, rather not used by anyone else is bad.

Then, the following are worth looking at as well:

• NixOS; it's quite different to all the others, perhaps we may call it obtuse by comparison. But, it has been going at it for the longest; heck, it's older than Ubuntu. And, in my humble opinion, is one of the main inspirations for the others. But, contrary to the likes of Fedora Atomic or Vanilla OS, it doesn't go all-in on OCI. Therefore, it might not be as smooth of a transition.
• Guix System; the answer to "What if we had FSF-compliant NixOS, but with actually good documentation?" Jokes aside, this is a cool and underrated distro.
• openSUSE Aeon; relatively new still, but perhaps already offers the most secure OOTB experience. However, from what I can tell, in terms of transition to OCI, it doesn't strive to be very revolutionary (as of yet). Fedora Atomic seems to be a relatively significant (and IMO exciting) departure from traditional Fedora. By contrast, openSUSE Aeon seems more like a ~r~evolution with a (very) small r. Though, one may argue this is mostly due to maturity. Consider openSUSE Kalpa if you're feeling particularly adventurous.
• uBlue's base images; Aurora, Bazzite and Bluefin are built from these. These are vanilla images with only hardware enablement, codecs, other RPM Fusion goodies and more that anyone installing Fedora Atomic would want on their systems anyways.
• Create your own; See this link if you know how to write containerfiles. See this link if you prefer yaml (.yml to be more precise) instead. The previous links were more focused on Fedora Atomic, this link offers Vanilla OS' answer.

Other distros found on lists like this one didn't make the cut for various reasons; sometimes it's just because I haven't heard enough of it.

Do I need to shift my expectations of an immutable distro even more?

Uhmm..., I don't know exactly what your expectations are 😜.

FWIW, from what I gather, either (something based on) Fedora Atomic or Vanilla OS should be right up your alley.

Important elaboration. Much appreciated.

I'm mostly oblivious of what's required to run an ISP. But you mentioned servers yourself. Do you install Linux Mint on your servers?

Fair. Even if some may dismiss it as anecdotal (N=1), I do think it's valuable. Thank you.

with Mint when the next release you are more likely than not going to have to re-install

First time hearing this. Got anything to back that up?