Unable to perform a one-to-many join between two feature services stored within the same hosted feature layer in ArcGIS Online using the Add Join or Join Field tools in ArcGIS Pro.

Workaround

Run the Join Features tool in ArcGIS Online Map Viewer with the tool's 'Join operation' set to 'Join one to many'.

Do note that the Join Features tool will apply the join to a new output table instead of one of the tool's input tables as the Add Join and Join Field tools do.

Steps to Reproduce