Is there any plan to enable users to use their own network analyst services (oublished by ArcGIS Server not standard ArcGIS Online routing services) to find shortest routes in the next release of Collector for ArcGIS?
If you are administrator of your AGOL org or Portal, you can configure utility service - Directions and Routing and use your own routing service. If I remember right, Collector should leverage it. Have you tried this one?
Configure utility services—ArcGIS Online Help | ArcGIS
To configure Directions and Routing, enter the URL of your route service, for example,https://gisserver.domain.com/arcgis/rest/services/World/Route/NAServer/Route_World.
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