You can boot a live image and try to repair the installation or you can restore the vm. Looks like disk or module is missing or both.
Can you do ls for /dev?
The VM has been running for almost a year, nothing changed.Did you change anything in the VM config before this happend? Is it a new VM or converted from another type like .vmdk, please share your vm config (/etc/pve/qemu-server/<id_of_your_vm>.conf)?
AFAIK if this is a unifi controller, it should make backups of the configuration on its own which means in the worst case you could just restore it that way.