first of all I restored the most recent petitboot (spiboot-20221228.img) according to this guide and tested to directly boot and install dietpi on a fresh SSD.
So I flashed the recent dietpi image DietPi_OdroidC4-ARMv8-Bullseye.img.xz to the SSD and it booted straight away. Somehow there was a small vat partition on /dev/sda2, after manual deletion of /dev/sda2, I triggered a resizeFS and the dietpi setup runs smoothly after reboot. So for fresh installs on HC4 we could state somewhere in the documentation that a direct sata boot is possible.
Next I will try to restore the data from the backup or clone the SD card as stated in the following post Odroid N2/HC4 | Add support for petitboot>USB boot · Issue #5634 · MichaIng/DietPi · GitHub text*