When verifying a detached signature Kleopatra and the original file does not exist Kleopatra does not ask the user to identify the file that should be verified but fails with an Input/Output error:
On Linux the behavior is different and it falls back to the old decrypt/verify dialog which offers a file selection. But for usability I think it would be best if we directly show a file selection dialog for the user to pick the file that should be verified. This would be most intuitive in my opinion.