The easiest way I can think of is to rename the initial map frames (Map1-Map9) as Map01, Map02, Map03, ..., Map09.
This will ensure all the maps are in order in the dropdown list.
Definitely the way to go. You may be able to quickly rename them all using a bit of arcpy and regex, too.
aprx = arcpy.mp.ArcGISProject("CURRENT") for lyt in aprx.listLayouts(): pad_name = re.sub(r'(?<=Map)(?=[1-9])(?![1-9])', '0', lyt.name) lyt.name = pad_name