Pop-ups configured in ArcGIS Pro change when the feature service is added into a new Map Viewer?

[Hayley]

I have published a feature layer and the pop-ups were configured in ArcGIS Pro before publishing. 

When I check the pop-ups in the Visualisation tab of the published layer, they have honoured what I configured in Pro.

However, when I add the feature layer using the service URL into a blank web map in the new Map Viewer, the pop-up configuration is lost. The pop-ups stay consistent in Map Viewer Classic. 

I am confused because I configured the pop-ups in Pro. 

How do I get the pop-up configuration to stick in the new Map Viewer when using the service URL?

[KaseyCox]

THANK YOU Russ!  I will learn how to add the layer item to web map rather than the service!