I have wondered if there is currently an equivalent of df = mxd.activeDataFrame in ArcGIS Pro? I can't find anything up to now. I would have expected something like aprx.activeMap, but that doesn't exist on the ArcGISProject object.
activeDataFrame is such a crucial tool in working with arcpy in ArcMap, that I am slightly stumped to see no obvious equivalent in Pro. Yes, you can use listMaps to get to the maps, but that doesn't tell you anything about which one is currently active / in front view.
Of course, with multiple possible maps and layouts, there may also be a layout "active", but there should be ways to deal with that. Maybe a more generic aprx.activeFrame? ... with some possibility to test what type it is.
Anyway, is there anything I missed?