After an interrupt due to a hardware defect that was fixed by our supplier, I could continue with our proof-of-concept of Harvester HCI (to avoid migrating out test infrastructure to ESXi 7.0). After some more search for the error, I found the following resource on reddit:
djf_jeff’s answer caused me to look into the bios and (for me unexpectedly) hardware virtualization was switched off. Since enabling it, the test VMs I created are running - without any other intervention. The take-away: Harvester improves UX of KubeVirt (and a few other tools), which in turn lets VMS behave like k8s deployments. There are a couple of problems still to solve, but imo Harvester looks very promising.