KDE

Keep the defaults. Depending on the distro change to double click. That's it.

My experience is that it's similar enough out of the box that it's fine for more users. Unless she's really disturbed by anything that doesn't look absolutely identical, having some noticeable differences is good as it's a bit of a reminder that you're not on Windows but works similarly to Windows.

Like, you could go all on and install a Windows 7 or 10 theme and make it look like Windows nearly pixel perfect, but then you set the expectation that it works exactly like Windows and that leads to disappointment as soon as the illusion falls apart, and she also won't learn to explore new features if it's presented as diet Windows. You want it to look familiar, not sell a lie or an illusion.

I got my mom to use Linux for a while, it was hard to get her to move on from XP to 7 and then 7 to 10. The switch to Linux went comparatively smoothly, because it was clear from the start it's not Windows, it doesn't work like Windows. But it retained the familiarity of the start menu, the task bar, the tray icons, so she felt comfortable using it and exploring it but came in with an open mind and without the expectation and frustration that came with trying to do something and realizing it's not there. She knows she won't just download a .exe and run it, that she has to use Discover.

Change from single click to double click to open!

I guess theming would make a lot of the work, I don't remember the names but there are a few plasma themes that aim to mimic windows 10 and 11. If not the entire theme, the icons at least would make it way more intuitive.

For the office suite you might want to check out OnlyOffice(or even freeoffice), it probably looks more modern and less jarring than libreoffice for someone coming from recent versions of MS Office.

The start menu also has versions of it more similar to the windows one, but the standard one Is much better, maybe it's a change she can get used to.

Make sure the desktop is in Folder View, so she can put files and folders on it, and set Dolphin's view to the one she's used to, icons or details.

I'm not sure for gaming, but maybe check beforehand if hers work on kubuntu.

Finally I'd make a post-it explaining the names of programs: dolphin - > file explorer, Kate - > notepad, ark - > 7zip and so on. The most frustrating thing is looking for a program that should have an obvious name and finding only unknown nicknames, it takes a while to get used to!

Give her Ublock secretly.

It doesn't have to be 1:1. Make sure to install drivers, set up proton (so that proton is used by default), Install Only Office (because it is the most appealing to Microsoft office user) and if she really needs it create web apps for Microssoft Office and ensure that they can be launched from the desktop, taskbar, and start menu. Also Install adblockers and whatnot on her browser. Just nothing that could interfere with her workflow. So Ublock, Sponsorblock, CleanURL, I Don't Care About Cookies, and Return Dislikes to Youtube. Also use this hardening script because it makes Firefox secureoit of the box and in my experience has never gotten in my way: https://github.com/hnhx/user.js

Install Kubuntu, change the wallpaper to a grab of a BSOD and she'll feel right at home.

Double click, classic app menu. Onlyoffice as office app.

Make sure to install Nvidia drivers if she has an nvidia card ex: sudo nala install nvidia-driver-535.

I love Plasma but it's worth considering Linux Mint with Cinnamon. Let her try each with a Ventoy live USB on her computer.

hmm, that's a tough one, the KDE defaults are pretty good these days. maybe try to identify any points of friction and configure KDE to be more similar to Windows. a few that come to mind:

Ensure double-click is selected for opening files in Dolphin

Ensure Flatpak is working in Discover

Windows users are used to desktop icons, if she wants that, set the desktop to Folder View (or teach her the glorious ways of Application Launcher and a clean icon-less desktop)

Play around with the different options for Application Launchers, Taskbar, Task switcher.

Set up virtual desktops, and the desktop switcher applet? it's such a killer feature. just tell her about it so she doesn't get annoyed all her windows are suddenly gone. also maybe disable "scroll on desktop background to switch virtual desktop"

I'm not sure if setting up a Windows-like theme is a good idea or not? If everything looks "the same" she'll expect it to work the same way, and get annoyed whenever it doesn't.

Because it's KDE, remind her that if there's something she doesn't like, chances are she can change it.

OH, and use dark theme! Breeze Light looks kinda meh and old fashioned. Breeze Dark looks slick and modern

What's more important than KDE is the applications you mentioned..

Gaming is (ironically) the easiest these days. Assuming she uses Steam, and her games are working through Proton

Which browser does she use, and is she willing to switch? Although every modern browser is available and running well on Linux, there's is a slight caveat for Google Chrome: (last I checked) Google Chrome is not available in most software repos. Chromium is available, but not Google Chrome. Because Chromium is degoogled, it's lacking certain features, most importantly Google Sync (password etc). You can still download and install Google Chrome from the Google website, it's just a bit more cumbersome than having it easily available in the repository. And anyway Firefox is superior xP especially once Google implements ManifestV3 which disables (good) adblockers.

The office suite can be the hardest part. Does she use Microsoft Office? Microsoft Office doesn't run on Linux, so she would need to swap. The good news is that she can try out the alternatives while still on Windows, to see if it's a deal-breaker or not.

• OnlyOffice ( change the setting to make each app a separate window )
• LibreOffice
• WPS Office (not open source)

KDE Plasma is a great use for that!

Mostly keep the defaults, but change single click to double as others mentioned, disable scroll action on desktop (switch workspace), disable scroll action on taskbar (cycle through opened windows) and that's pretty much it.

I like to keep my plasma desktop as close to my win 11 desktop as possible, more for consistency than and personal preference. Here are a few tips:

There are a few decent Windows 10/11 plasma themes. I would stick with the breeze window decorations though because the 3rd party ones often don't scale properly.

Change the icons. There are a ton of options that would be more windows like. Consider changing the cursor as well. I like the breeze cursor but it screams 'this isn't windows!'

The default start menu is a little weird. I typically change it out for the one that looks more like the Win9x start menu.

You can change the click behaviour of the task bar to behave more like windows.

Personally I find the gnome file browser a little more user friendly than Dolphin, so swapping that as the default file browser might be a good idea.

OnlyOffice is an alternative to LibreOffice that is a little closer to Office

If she doesn't have Nvidia gpu, then install her the LMDE5 and here's why: https://forums.linuxmint.com/viewtopic.php?t=374128

It'll save you all the time spend customizing the UI as it should always been done by the end user.

KDE is great but requires tinkering so therefore I don't recommend for the first-time users.