QDragManager fails when dragging more than one url.
If a drag representing files is initiated that represents more than one draggingItem, the only way to represent this is using QMimeType::setUrls().
The URL mime type is required to send files to Finder. [Anecdotal: other mime types work fine]. When the drag is executed, cocoa throws an exception, leaving the QDragManager in an indeterminate state.
I've attached a sample application and a screenshot of the error "QDragManager::drag in possibly invalid state".
With the release of macos 12.15, it appears that enforcement of "1 draggingItem per pasteboardItem" has started. This was hinted at in 12.14 release notes, https://developer.apple.com/documentation/macos_release_notes/macos_mojave_10_14_release_notes/appkit_release_notes_for_macos_10_14