Inability to install system, lack of WiFi drivers

[pebcak]

Perhaps you could do an offline install.

Then once booted to your installed system, connect your phone to the usb port and use its internet connection to install the required packages.

When you got WiFi up and running, you could install KDE and remove Xfce.
Perhaps the more convenient way would be to create a new user for the “KDE Plasma user”.

See the following articles for how to install and/or remove a desktop environment:

https://discovery.endeavouros.com/desktop-environments/how-to-install-desktop-environments-next-to-your-existing-ones/2021/03/

https://discovery.endeavouros.com/desktop-environments/removing-a-desktop-environment/2021/03/

Edit:
Please have a look at this post as well:

Switch from default Xfce to Plasma

plasma is probably the easiest DE to install. Simply install the group plasma. Then enable sddm and remove xfce and lightdm. I haven’t tested it but something like this: sudo pacman -S plasma sudo systemctl enable sddm.service -f sudo pacman -Rc xfce4 xfce4-goodies Be careful and review the list of packages to be removed carefully. It is a clean install, don’t login to the xfce4 session. Instead log into the TTY and do it there. That should keep your home directory cleaner.