Install Fedora with KDE.
Install Firefox, Thunderbird and Chrome.
Install uBlock Origin, Privacy Badger.
Install LibreOffice & bookmark Google Docs.
Install multimedia support, h264/h265, VLC/mpv/ffmpeg, enable DRM in browser.
Install Steam if applicable.
If they have a printer, connect it and show them how to print a page.
Configure & tweak KDE to be cleaner & more user friendly (its already near perfect out of the box). Show them how to manage wifi/lan connections.
Stick with Intel & AMD hardware, Nvidia drivers breaks on most kernel updates (and it messes with luks/secureboot/dracut). Intel & AMD, Just Works.
Educate the user on how to do Software Updates, install/remove software, how the file explorer works, maybe some terminal stuff if they seem inclined. Give them a high level overview of the benefits of linux.
With Fedora and KDE you can accomplish 95% of your computering needs, including software development. Only a handful of games & creative softwares don't work.
It will only take 6 months to have them permanently converted.