Oh, I see, you’re using virtiofs exported filesystems, not full (raw) disks.
Hmm, then there may be an issue or some extra stuff needed to get WinFSP to handle it correctly. At the Incus level we definitely exported multiple virtiofs drives and that can be accessed just fine from Linux VMs, so it’s likely an issue or missing config with the Windows implementation (WinFSP+virtiofs)