Linux

I'm personally a fan of Debian. Default KDE isn't bad looking from what I can remember (I personally don't use it - I neither hate or love it just because I love XFCE). I'm personally a big XFCE fan, but you do have to do some work to get it working good, and there are still jank parts here and there.

While no distro is completely set and forget, I think Debian Stable is as close as you can get. Once you install it and get it working the way you want (depending on your setup, you might encounter minor issues as with any distro), it will pretty much stay that way until you upgrade to the next version, and you can go up to 5 years before upgrading.

I would recommend you use the KDE (or whatever DE you want) live installer, though, as the default installer is quite unintuitive. You can find it in the list of installers at https://www.debian.org/distrib/.

I've never used Kubuntu specifically, but I would personally avoid Ubuntu these days if just because of Snaps. Also, Ubuntu is heavily bloated - base Ubuntu is almost unusable in a VM now, while vanilla GNOME and PopOS run well in VMs on the same machine. Personally, when I need to test Ubuntu builds, I always prefer working with PopOS.

Overall, I'd say if you don't end up using Debian (I don't blame you - while I like it, you might not), just please don't use anything Ubuntu-based that isn't Mint or PopOS.

Kubuntu is excellent for the stability imo. Super sane and low-demand defaults make for a reliable/enjoyable experience
I only use gentoo now so I can't offer suggestions other than maybe alpine for servers

Fedora KDE is a good one.

https://fedoraproject.org/kde/

Debian is always the forgotten choice. You can install kde at time of install. It's stable and can be upgraded in the background automatically even between major versions. Doesn't have snaps making hell for the user. For any apps they need the newest version of Flatpak is right there in Discover software center.

Well there are no operating systems that you can install and forget, unless they never plan to go online with the machine. They all need updating which can be set automatically. The only problem is if it requires manual intervention, sometimes updates don't go as planned, then a roll-back might be necessary. They could try an immutable linux distribution if they are worried about screwing up their installs or something. Fedora kinoite may be their thing, or Bazzite which is based on that.

Best I can offer is Hannah Montana linux

Kubuntu is just really well polished. It works really well and stable nowadays. Only downside is snap.

Also have a look at Linux MX. Also very well polished and some really good tools.

Focus on the DE instead of the distro. There used to be one that has "windows look" as a goal.

If you want a set it and forget it distro to never touch his computer again, then consider going a Ublue distro. Aurora (only KDE), or Bazzite (choose the KDE image) if he does gaming.

If you want windows with sex apeal, the KDE desktop environment's treated me pretty well. I'm using Fedora, though you could get it from other distros too

I want to try something windows like with more sex appeal.

Elaborate?

I don't want to have to touch this computer again.

This person will undoubtedly need help and if they can't help themselves you will be the one helping them. Mint is best-case for ease of use so your requirements are a bit contradictory.

Fedora KDE edition or OpenSUSE Tumbleweed/Slowroll. Otherwise could try Aurora.

I avoid Ubuntu base because it is slow to update packages, and the inclusion of Snap packages are a no from me.

Another vote for Aurora.

Universal Blue in general has been really solid, I remember one time in the last year or two when there's been any need for manual intervention. And that came with a notification after boot, with a link to instructions that were all copy-pastable as-is to the terminal.

MX Enlightenment Respin has a unique and excellent look. Add some Propaganda Wallpaper Tiles to further enhance the vibe https://github.com/BenjaminHCCarr/PropagandaTiles

ChromeOS Flex. Very low maintenance.

I used Kubuntu in college quite a bit and very much enjoyed it. No issues myself.

Of course, Linux mint KDE edition is a suggestion, but it'd be easier for your friend to find help online with Kubuntu as they can just google the name instead of knowing what's a plasma issue and what's a mint issue.