You didn't state what Mac you're using.
If you're using an M1 or M2 based Mac, you cannot virtualize macOS in Fusion. Virtualizing macOS on Apple silicon (M1/M2) can only be done using Apple's high-level virtualization framework which Fusion doesn't use. (It uses the lower-level hypervisor framework.)
If you want to create a macOS VM on Apple silicon, you can try VirtualBuddy, UTM, or Parallels. However, the VM will be severely limited in what it can do. (I.e., no snapshots, no split disks, etc.)