When we try to add another disk to a running VM, we get a list of SC's, that is not filtered, so, in addition to listing the usefull SC's, the S3 backed SC's are also listed, like RGW and noobaa.

4.14.6

100%, at least when the VM is running, I have not tested with a powered off VM, or with alternative disk controller drivers (only tested with scsi)

1. Create a fedora VM from template
2. Start it
3. Add another disk
3.1 Source: Blank (Creates PVC)
3.2 Type: Disk
3.3 PVC Size: >=1G
3.4 Type: Disk
3.5 Interface: SCSI
3.6 StorageClass: Select either RGW or NooBaa, the result is the same
3.6.1 I have not tested the cephfs SC, as of creating this ticket, but I assume it also does not work, because it's not possible to create a PVC backed by CephFS, that is in "volume mode: Block"
3.7 "Enable preallocation" can be false or true, the result is the same

"Disk" is created, but looking in the yaml, the status is:
status:
...
  volumeSnapshotStatuses:
   ...
    - enabled: false
      name: disk-gigantic-wildebeest
      reason: PVC not found

Only valid SC's should be listed in the "Add Disk" UI, or if that's not possible, then at the very least, SC's we know are incomptable, should be excluded, like rgw and noobaa.