Is there a way to display a link to the related records directly in the popup information, similar to the way it works in the portal map?
Yep. Just check this box when Configuring Popup:
Not sure where that configuration is. Is that the latest version of AGOL? We are using AGOL internally, at version 10.5.1.
That is the AGOL Map Viewer app when you configure your layers popups.
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