Ok, never mind. I went in a loop to [ armbian-config/switch to other kernels, chose the next newer kernel, apt update && upgrade ], and after a few rounds I got to:
Armbian 22.11.1 Bullseye with bleeding edge Linux 6.0.10-sunxi
In which everything works as it should ! :-)
shutdown -h 0 is now turning it off.
Cheers,
George