macOS FileProviderExtension prevent file creation via NSFileProviderUserInteractions

Question

My FileProviderExtension should allow creating folders in the root level, but not files. Is there a way to achieve that?

I tried creating a NSFileProviderUserInteractions entry like

<dict>
  <key>ActivationRule</key>
  <string>(action == "Create" OR action == "MoveIn" OR action == "CopyIn") AND destinationItem.itemIdentifier == "NSFileProviderRootContainerItemIdentifier"</string>
  <key>SubInteractions</key>
  <array>
    <dict>
      <key>ActivationRule</key>
      <string>TRUEPREDICATE</string>
      <key>Alert</key>
      <dict>
        <key>LocalizedRecoveryOptions</key>
        <dict>
          <key>Cancel</key>
          <string>OK</string>
        </dict>
        <key>LocalizedSubTitle</key>
        <string>Files cannot be added to root level.</string>
        <key>LocalizedTitle</key>
        <string>Forbidden action</string>
        <key>RecoveryOptions</key>
        <dict>
          <key>Continue</key>
          <false/>
        </dict>
      </dict>
    </dict>
  </array>
</dict>

but this prevents creation of both files and folders in the root level. How to just prevent file creation?

Probably relevant: Apple NSFileProviderItem.h states for 'Create':

'Create': creating an item (available in macOS 12.0 and later) The Create action will be evaluated when the user creates a new file or folder in a system Open/Save panel. The sourceItem is the file/folder being created. The only field that is populated for this item is the filename. The type of file/folder, size, etc, are unknown at Create evaluation time. The destinationItem is the directory which the file/folder is being created within.

Does this mean that whether it is a file or a folder which is being created is unknown at 'Create' time? I find that quite weird and if that is the case then this cannot be supported?