There should be a keyboard shortcut for each of this three options in this dialog box (see the screenshot):
Save (Speichern) = Return, Enter
Cancel (Abbrechen) = cmd+. or esc
Don't Save (Nicht speichern) = cmd+delete (it used to be cmd+d)
Save and Cancel work fine, but Don't Save doesn't work at all. Is there something I'm missing or has Affinity forgotten to implement this system wide standard keyboard shortcut? 😲