With many thanks to alias Tu®tle on discord who did all the animation.
This dialog pops up and on progress checks if a variable check is True before cancelling the animation and dismissing the dialog.
THE COUNT (cnt) VARIABLE IN THIS EXAMPLE IS JUST TO ILLUSTRATE THE CONCEPT OF DISMISSAL
For real implementation with your own check use the following progression function in the example instead:
def progression(self, *args):
if self.check:
args[1].text = "Finished"
Animation.cancel_all(args[1], 'dots')
App.get_running_app().root.busy_dialog.dismiss()
elif self.timeout == 20:
args[1].text = "Timed out"
Animation.cancel_all(args[1], 'dots')
App.get_running_app().root.busy_dialog.dismiss()