A common use case with Kleopatra is to move a key to a smartcard:
- Create key
- Move the key to card
- Make a backup of the public key
- Delete the key (private and public)
- Import the public key
- Set the imported key again to ultimately trusted.
Unfortunately we need to handle the key stubs at least with GnuPG 2.2. This requires that one first needs to hit F5 in the card dialog (which creates the stub but does not give any visual feedback) and then hit F5 in the key listing so that the imported will be marked as having the private key. Only then the key may be marked as ultimately trusted.
Not everyone known when to hit F5.
It would also be possible to add an option to remove only the private key - this would in fact be easier to understand for the user. Maybe by collecting the moved (sub)keys and finally offer to delete their copies.
Update 2022-04-19: As discussed, the destructive operation to delete the private key should be confirmed by the user by entering some text, e.g. "delete".