I have a rock as vm and it responds to a shutdown (I think it is in the end a stop…).
I did have same issue at first. Not sure what changed.
But to start I put in a shutdown timeout of 3 so it will not wait for the host timeout of 120 seconds.
I also tried for a moment a systemd oneshot script that can trigger the rock shutdown api.
Search for run-before-shutdown.service and in the exec use the “http://rock.local/1/poweroff” shutdown call.
(The systemd is ofcourse installed on the proxmox host)
I’m running Roon (Rock) as a VM on ProxMox and have no issues with shutdown. I use PBS for backups and that is running on a older PC as bare metal. My backups run nightly without error even though I keep all VMs running while the backups are performed. I do question my sanity though as I probably have zero need to backup the Roon VM.