CH8 doesn't start installer on HPE DL20 Gen10

I tried via USB-Stick as well as via iLO-mounted Image.
Safe mode doesn't work at all, it disables IOMMU and thus the (kernel) boot stops early stage.

The normal "install" ends up with:

[ OK ] Started Update UMTP about System Runlevel Changes.

And gets stuck there.
I'm able to switch to other consoles, a warm reboot is possible and everything looks fine - just the installer isn't starting.

I removed the E208 SAS controller as well as reducing memory from 32 to 16 GB and unplugging network cables. Nothing helped - it always stuck there.

7.6 though is booting fine and the installed OS works also - since the change to 8 it stucks there.

Any ideas?
Attached is the output of dmesg.