The plasma-desktop package seems to be missing from this update - it is no longer in the Testing repos:
mbn info plasma-desktop -q
Branch : archlinux
Name : plasma-desktop
Version : 6.6.2-1
Repository : extra
Build Date : Wed 04 Mar 2026 08:26:01
Packager : Antonio Rojas <arojas@archlinux.org>
Branch : unstable
Name : plasma-desktop
Version : 6.6.2-1
Repository : extra
Build Date : Wed 04 Mar 2026 08:26:01
Packager : Antonio Rojas <arojas@archlinux.org>
Branch : stable
Name : plasma-desktop
Version : 6.5.5-1
Repository : extra
Build Date : Wed 14 Jan 2026 07:11:15
Packager : Tomaz Canabrava <tcanabrava@archlinux.org>
Seeing the message that it was now an orphaned package had me scratching my head, however I made the silly assumption that maybe its functionality had been merged into another part of Plasma (possibly plasma-workspace), so I took the risk of removing it after the update:
[2026-03-12T08:11:46+1100] [ALPM-SCRIPTLET] foreign plasma-desktop
[2026-03-12T08:15:03+1100] [ALPM] removed plasma-desktop (6.5.5-1)
Of course, my assumption was wrong. When I rebooted, I ended up with a black desktop.
I resolved the situation by switching to a TTY & installing the plasma-desktop v6.5.5 package stored in the cache:
sudo pacman -U /var/cache/pacman/pkg/plasma-desktop-6.5.5-1-x86_64.pkg.tar.zst
[2026-03-12T08:30:04+1100] [PACMAN] Running 'pacman -U /var/cache/pacman/pkg/plasma-desktop-6.5.5-1-x86_64'
[2026-03-12T08:30:19+1100] [PACMAN] Running 'pacman -U /var/cache/pacman/pkg/plasma-desktop-6.5.5-1-x86_64.pkg.tar.zst'
[2026-03-12T08:30:24+1100] [ALPM] installed plasma-desktop (6.5.5-1)
I now have a desktop again.