Joplin 2.7.15 (prod, linux)
Client ID: ee541165951b402fa2fcd4ef9972af3c
Sync Version: 3
Profile Version: 41
Keychain Supported: No
This problem applies to Windows 11 as well.
I have a dozen or so notebooks on the root level. About half of them have sub-notebooks. If I accidentally drag a root notebook down, it will be added into the neighboring notebook as a subfolder. Then each attempt to drag the notebook out will simply make it a sub-notebook of the closest notebook. I cannot move it back to the root level. It seems like there is no drop zone to place a notebook at the root level.
I normally use the macOS theme plugin, but I tested with it disabled and the problem persisted.