Thanks for your reply. Have you tested whether that will work? It looks like it may be for filters but I'll give it a try. Workforce doesn't support pop-ups at all, by design they said. There is a tab on the designer that lets you create links to other apps that are stored in a table. Then it is linked to a button on the mobile app workforce dialog. The lat/long are already available in the assignment table but are hidden. This is the default URL from the GUI for the S123 link:
https://survey123.arcgis.app?itemID=xxxxxxxxxxxxxxxxxxxxxxxxxxxxx¢er=${assignment.latitude},${assignment.longitude}
so the coords are in there but I will try the folder param you suggested, thanks.