For anyone having the same issue. I managed to import the VM from GCP like this:
- Export it from GCP as qcow2 file. (Create an Image then export this to a bucket then download the file from the bucket)
- Create a Linux VM in Proxmox and assign it a (small) HDD in qcow2 format.
- go to VM settings -> Hardware, detach the freshly created HDD. Do not delete it yet.
- locate the file in the filesystem. It will be called something like: vm-1009-disk-0.qcow2 (where 1009 is the VM-ID)
- replace this file with the qcow2 file of your GCP VM. Pay attention to use the same name.
- re-attach the hdd via the PVE GUI (Add -> Hard Disk and choose the file)
- check the boot priority in the options menu and make sure the hdd is the first to boot
Done.
You probably need to figure out the IP Adress from your dhcp server since root-login is usually disabled on GCP VMs (root does not even have a password).
Doing it this way, you do not need to edit any vm-config file or even use the console. The detach & re-attach part is so that pve figures the hdd sitze by itself.
Finally a word of caution. GCP VMs tend to have special apt-repositories configured, as well as google telemetry daemons etc. You should be very carefull if you plan to use this as a live-system of any sort.
I did it only as a backup after a big migration, so that we can still access the old system withouth paying for two servers.