TypeError: QgsRubberBand(): argument 2 has unexpected type 'bool'

[mathuin]

https://api.qgis.org/api/api_break.html#qgis_api_break_3_0_QgsRubberBand

The QgsRubberBand() signature has changed.

Thanks to this, I was able to fix the issue by importing QgsWktTypes from qgis.core and changing line 397 to:

        self.extent = QgsRubberBand(self.canvas, QgsWkbTypes.PolygonGeometry)

With these changes, I was able to create a reasonable-looking PNG. Hope this helps!