I did the upgrade, then the downgrade, and re-booted. It looks like plasmashell came back. My Application Launcher seems empty, but I was able to click on the K to run kinfocenter:
Operating System: KaOS (2023)
KDE Plasma Version: 5.27.80
KDE Frameworks Version: 5.245.0
Qt Version: 6.6.0
Kernel Version: 6.5.11-1 (64-bit)
Graphics Platform: Wayland
Processors: 8 × 11th Gen Intel® Core™ i7-1185G7 @ 3.00GHz
Memory: 15.0 GiB of RAM
Graphics Processor: Mesa Intel® Xe Graphics
Manufacturer: Dell Inc.
Product Name: Latitude 5420
I had to open the konsole (again no icon, just type konsole) to start qutebrowser.
Falkon did not start from krunner, though it appeared along with its icon as I started typing there, but from krunner, command line run falkon did work.
I had kservice6 installed and then I installed kservice and re-booted, and my icons in the application launcher are back and seem to work.
I did not remove kservice6:
pacman -Q | grep kservice
Paper cut: Plasma 6 System Monitor Sensor widget (plasmoid) does not show Core x Total Usage
But I would agree: The upgrade is safe. Thank you.