I’m upgrading my father-in-laws 2011 imac (Intel, amd GPU) to an ssd, 16GB ram, and planning on putting an immutable linux OS on it for him since he primarily uses the browser anyways.

Any recommendations for non-techy seniors/gotchas for installing it on a mac?

I was thinking fedora silverblue since GNOME should feel more familiar than KDE for him.

Definitely not just for handhelds. Check out Universal Blue images which are built ontop of Fedora Atomic (the immutable variant). Bazzite is an awesome gaming distro that’s rock solid. Bluefin is awesome for Devs and more technical people. But even for non-devs it’s awesome since the images are purpose build with and without all the devs tools. You pick your preferred DE (KDE or GNOME), and your graphics drivers.

Almost everything is setup for you that you would have to do mannually compared to Fedora Atomic, and additional quality of life tweaks are included as well.

Been running, Bazzite on my gaming rig for months now and it’s been great. Running the Cosmic/Gnome UBlue image on my framework laptop for months and its also been amazing.

But I’ve been looking at immutable distros as a more stable alternative.

If “stable” is used in the context of “intended use entails no changes/updates to packages found in the repositories in between ‘long supported’ point releases”^[1], then it’s important to note that an ‘immutable’ distro as such does not exist; or at least is far from mainstream*.

If, however, "stable", instead, is used in the context of “less inclined to cause breakage upon (perhaps more frequent) updates”, then indeed; ‘immutable’ distros can definitely be beneficial. Heck, I would even argue that they are successful at providing more stable experiences. This is actually implied merely by design. And, thankfully, the ‘immutable’ distros have been able to deliver on this promise.

But, it sounds to me like it’s more adapted for smaller devices and IoT, like the Steam Deck or similar handheld devices.

They, indeed, make a lot of sense for these use cases. However, the use of ‘immutable’ distros on desktop is also pretty well established. Even if it’s currently (relatively) niche.

Have you installed an immutable distro on your PC?

Yup. Over two years ago, I switched cold turkey from Windows to Fedora Silverblue without any prior Linux experience. I’ve been very happy with it ever since. However, since over a year, I’ve been on uBlue. These are recommended over Fedora’s own images for a multitude of reasons; one of which being better on-boarding.

What distro did you use?

As previously mentioned; Fedora Silverblue. Back then, and even today, Fedora Atomic has been one of the most mature iterations. Other mature ‘immutable’ distros (i.e. Guix System and NixOS) require a lot more know-how by comparison.

What was your experience like?

I simply don’t see myself use traditional distros beyond special use cases. Literally all of my experiences with (semi-)rolling traditional distros^[2] (that I have engaged with through dual booting) ended with an unbootable system. By contrast, besides my first week, I can’t recall the need to resort to Fedora Atomic’s built-in rollback functionality to combat a non-booting system. It’s just been such a pleasant experience.

1. Besides those related to security.
2. Which include the likes of Arch, EndeavourOS and Nobara.

But, it sounds to me like it’s more adapted for smaller devices and IoT, like the Steam Deck or similar handheld devices.

There are plenty of desktop focused immutable Linux distros. With Fedora Sikverblue/Kinoite probably being the most prominent one, but there are also Vanilla OS, the ublue distros and the one I’m personally using, (openSUSE) Aeon. NixOS technically counts too I think, but that one has it’s whole own philosophy/structure that extends way beyond just being immutable

What were the pros and cons according to you?

Pros: increased stability/less risk of breakage, sepaeation of base system/apps that will be more intuitive to many non-Linux users, (Flatpak) apps tend to always be the newest version
Cons: still some smaller pain points around app integration, some flatpaks might have some features that don’t fully work or you might need to change a permission (this has gotten a lot better already though), less suited for tinkerers

From my personal testing experience I would say the concept is solid but the existing distros are not there yet, with some missing features, minimal documentation and several rough edges in their containerisation approach (as in: some features and things not working because the container wasn’t well adapted to the immutable OS yet).