Linux

Best I can offer is Hannah Montana linux

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.

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.

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

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.

Fedora KDE is a good one.

https://fedoraproject.org/kde/

Get an immutable distro. You’ll never need to touch it again.

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.

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.

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.

I used to recommend Ubuntu. Now that immutable distributions exist, I prefer to recommend openSUSE Aeon or Fedora Silverblue to new users. However, check this website before installing Linux.

https://endof10.org/

Linux. Mint.

Everytime.

Maybe Aurora by Universal Blue?

It's based off of Fedora Silverblue, so it's atomic, rock solid and basically guaranteed to work (more secure by design as well). But uses KDE Plasma instead of Gnome and has a bunch of improvements here and there, including proprietary codecs and Nvidia drivers preinstalled (latter depending on the image you choose)

ZorinOS or the recent AnduinOS can be very Windows like with modernish windows sex appeal as you call it.

Edit: If a gamer you could add Nobara with its own theme or bazzite with KDE.

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

Every time I've tried Kubuntu it's been a mess. Though it's been a couple years since I subjected myself to it. It's still going to use Snaps, so there's that.

If they want bulletproof and up to date, Fedora KDE.

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.

You have had many answers, all of them revolving around Debian / Ubuntu. Yet it doesn't give the "like-windows" esperience. It's More like "slightly windows-flavored Linux".

For a more Windows-like Linux, which helped me transition easily because I retained muscle memory, is Zorin OS.

I think you should cruise this guy's channel:

https://www.youtube.com/channel/UCg6gPGh8HU2U01vaFCAsvmQ

He's very fair and uses all operating systems. I'm almost certain he's had a video on this exact question.

Mint is da only way

Fedora Atomic (immutable OS), install it and you can swap between Atomic, Kinoite, Bazzite, and any other atomic distribution easily.

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

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.

I personally like mint and pop!os for new users, but for this user I want to try something windows like with more sex appeal.

what don't you mean by "sex appeal"?