Adding a new disk to a VM using 'oc patch' causes a warning for the VM in the console that does not go away until the VM is restarted:
Warning alert: Pending changes
  the volumes replacement is effective only after restart
     Details > Boot disk

Adding a new disk via the Console does not cause this warning.

OpenShift Virtualization 4.18.2

Add a new disk to a VM using 'oc patch' with a YAML file, such as this:
spec:
  template:
    spec:
      domain:
        devices:
          disks:
          disks:
          - name: rootdisk
          - disk:
              bus: virtio
            name: cloudinitdisk
          - disk:
              bus: scsi
            name: disk-magenta-haddock-53
      volumes:
      - dataVolume:
          name: fedora-01-volume
        name: rootdisk
      - cloudInitNoCloud:
          userData: |
            #cloud-config
            chpasswd:
              expire: false
            password: redhat
            user: fedora
            runcmd: []
        name: cloudinitdisk
      - dataVolume:
          hotpluggable: true
          name: dv-fedora-01-amber-aardvark-83
        name: disk-magenta-haddock-53

1. Create and boot a VM
2. Add a disk using a patch file (as described above)
3. Observe the warning in the Console that the boot disk has changed (it hasn't)

The warning message appears and does not clear until the VM is restarted.

The disk should be added without a warning, like it does when you add the disk via the Console.