Blog for how to do it within ArcGIS Pro: https://community.esri.com/groups/applications-prototype-lab/blog/2019/03/05/distributive-flow-maps-...
Actual GP toolbox location: http://apl.maps.arcgis.com/home/item.html?id=f3aeafd89ae54fa1842c9e81e26025dc
Blog for how to do it in ArcMap: https://community.esri.com/groups/applications-prototype-lab/blog/2013/08/26/flow-map-version-2
Actual GP toolbox location: https://www.arcgis.com/home/item.html?id=04fa6ed8746b451892f339011aaf989d
These toolboxes work the same way. You can model flow of goods, planes, passengers, money or whatever from one location to many or from many to one. The quantity of goods are encoded on the "many" features. The single feature whether it is the source or destination is just starting or ending point. The tools names the single location the
Source and the many locations the Destinations but it works either way.