I suspect this will be caused by some missing bits in the QETH
emulation, ...
Yes, me too. I think the QETH emulation might need to respond to ARP packets.
... Does it fail
to even download the install.img or does lose the IP a bit later?
No, there is no network activity at all, the IP is never set.
It would be good if CTCM were fixed, imho CTC is still the simplest and most reliable
network interface in Hercules. Though as I said it isn't just the installer, an
installed Fedora s390x has the same problem. Things have got better over the past few
releases, in 34/35 the CTC wasn't even activated, one had to use znetconf.
Ian