Sparkle: Closing MuseScore terminates update on macOS
The Sparkle updater on macOS is in a separate dialog to MuseScore's main window. However, if the user closes MuseScore's window during an update then it also closes the Sparkle dialog, which terminates the update.
Keep the Sparkle dialog open even if MuseScore is closed (i.e. the Sparkle dialog should not be a child of MuseScore's main window).
Make the Sparkle dialog modal, so it is not possible to close (or interact with) MuseScore's main window during an update.
Simply provide a warning not to close the main window during an update.
Note that the WinSparkle updater on Windows has the opposite behaviour. On Windows it is possible to close MuseScore without terminating a WinSparkle update, and in fact you are required to do so as the installation will not complete if MuseScore is running.