> Is it possible to edit a WFS hosted in ArcGIS online in QGIS?
The discussion forums on GeoNet are for the ArcGIS Platform, not QGIS. You should try getting support for QGIS starting with this resource, https://www.qgis.org/en/site/forusers/support.html
Hope this helps,
Or with StackExchange.
But the underlying question (which is completely valid here I think) is just how locked down is ArcGIS Online as a collaboration tool with non-ESRI products? It's one of the main reasons I am moving to PostGIS for my collaborations.