Linux

Fedora Atomic desktops, specifically Kinoite with KDE6 works well for me, and is basically unbreakable due to the way it works.

Linux mint is a good, "click first" distro that won't break without root + will be easy for her to use. For something with a more modern desktop and more recent updates, Bazzite is really good at just working and (in my experience) has never broken

Any of them. Just don't give the root password.

Aurora by Universal Blue. She will be unable to break it, and it's so freaking easy to use and install.

I’m gonna be the boring guy.

RedHat Enterprise Linux. (Or Rocky)

Most boring distro ever. Install it, turn on all the auto updates and be happy. Install something to take backups. Ignore any new major-releases, that laptop will die before the OS hits EOL.

Benefits:

• Boring. It’s their tool, not your plaything.
• Actually works
• Will be reasonably secure over time with minimal effort and manual intervention.
• If any commercial Linux software is required, it will most likely only be supported on RHEL or Ubuntu.
• Provides web browser and word-processing. And we don’t need anything else.

Drawbacks:

• Boring (for you)
• Not ideal for gaming

If you install anything else than RHEL-derivatives or possibly Ubuntu on a machine that someone else will use, you are both in for a world of pain. It has to ”just work” without intervention by you, and it needs to keep working that way for the next 5 years.

Source: Professionally deploying and supporting multiuser desktop Linux to a few thousand users other than myself.

Use Bluefin or some other immutable/atomic distro.

The upside is that it's rock solid and will likely never fail in a way that cant be easily rolled back. The downside being that it's slightly more complex to administer than a traditional distro model (which probably isn't a big problem if you are going to be administering your SO's PC for the most part.)

Bluefin is basically a more general desktop, less gaming-focused version of Bazzite. Bluefin uses Gnome, but there's also a KDE Plasma version called Aurora.

Mint.

I have my mum (67) and my partner using it.

Libre office and Firefox cover 99.9% of all the things mum actually does.

My partner uses blender, krita and audacity also.

Auto updates... Almost no tech support.

Since less techy people tend to use more the mouse/touchpad anyways, I would pick a hard-to-mess-with desktop environment like Cinnamon or Gnome. With KDE, XFCE and such you can screw panels really easily if you don't know what you're doing.
Slap Debian under it and there you go

An immutable distro would be a good choice. They are distros designed to be more resilient against failure. For a gamer, bazzite is a solid choice; otherwise, silverblue.

Any immutable distro would do I guess

I guess it depends what she does on her pc.

But ignoring that, Mint without sudo. Throw in flatpaks and appimages.

Immutable distros are probably fine too but in my experience they tend to be a bit fussy if you need to change something in the system config.

Ubuntu, always a solid choice for beginners but Gnome shell is a bigger change from windows conpared to Cinamon.

P.S. I have Mint on our TV PC and my SO handdles it without issues.

Aurora or Bluefin would be great, general purpose distros. They're based on Fedora Kinoite and Silverblue, respectively, so you get that atomic unbreakability with the addition of some handy software and easy, optional scripts via ujust.

I have Bazzite on a laptop specifically for this reason, so if I ever kick the bucket early, they will have a reliable and portable computer.

Does she want this?

If so then just set her up exactly what you have so you can easily help when there’s a problem.

If not then get her the computer she actually wants.

Any of the ostree variants of Fedora, be they Fedora Official or downstream ones like the Universal Blue family

I've got my wife and 5 year old on slackware. They wouldn't know how to screw it up if they wanted to!

I switched from ubuntu to debian when 12 was released and it's been fine. Only thing i was worried about was running WoW via lutris but had no issues.

So when my SO windows pc died we bought some newish parts and i installed debian on it as well. Also installed chrome since that's her browser of choice. She's still getting used to gnome, but all she needs is browser, WoW, and libreoffice, which is close enough that it hasnt been an issue. She doesn't even know how to update the system.

I recently set up Fedora Kinoite on my dad's laptop for him and he seems very happy with it. Kinoite is the atomic/immutable version with KDE Plasma by default. Once I'd set up a couple of things everything else he needs can be installed with flatpak (just make sure to set Flathub as the default and disable the Fedora flatpaks repo that ships broken packages all the time)

BLUEFIN.

Debian is good at being basic, generic, stable AND has an automatic security-update-in-the-background feature

The whole amount of instruction to give to Dear SO is just to reboot the machine if it ever seems to misbehave

If you're not going to give her sudo access then I'd say it'll be really hard maybe even impossible to screw up. Also maybe setup a cron job that'll do auto updates and if needed add in a check to make sure it isn't uninstalling anything. Also how about immutable distro.

I thought this was a request for Stack Overflow proof.

Then figured that was 'proof from pasting random crap from SO".

Then figured it's the same thing.

Any distro will be suitable, create yourself as the first user when installing (which will probably be added to the wheel/sudoers group or whatever) then create a new 'standard' user.

Most distribution defaults should be adequate.

For added safety, choose one that is immutable like, for example, Fedora atomic.