I attempted to install IncusOS on a HP EliteDesk 705 Gen 4.
After enduring a lengthy struggle with TPM and SecureBoot (found some good info), I managed to successfully install IncusOS, but it encountered the same issue as mentioned in the „Need help for incus os installation, about seed configuration“ thread.
That boot error message only triggers if systemd-repart fails or IncusOS thinks it’s running from a CDROM and there’s no install seed present. For a first boot, my guess is that the automatic partitioning is failing for some reason. Unfortunately in an early boot failure, the network isn’t up yet so we can’t grab journal entries.
If possible, I think it would be useful if we could see what the partition table for the installed disk looks like. If you temporarily disable Secure Boot in the BIOS, you should be able to boot a live image of your choice to grab that info.