Setup KDE Plasma 6.3 Beta on Arch Linux

 Just update /etc/pacman.conf as follows

#[core-testing]

#Include = /etc/pacman.d/mirrorlist

[kde-unstable]

Include = /etc/pacman.d/mirrorlist

[core]

Include = /etc/pacman.d/mirrorlist

#[extra-testing]

#Include = /etc/pacman.d/mirrorlist

[extra]

Include = /etc/pacman.d/mirrorlist

$ sudo pacman -Syu and relogin to Arch instance