Hi,
I'm struggling with the same issue. (See also my similar post here: https://community.esri.com/t5/arcgis-indoors-questions/custom-attributes-for-events/m-p/1335688 )
I tried to use the existing fields "subtitle" and "long name" to create links (e.g. to website to register for an event), but they are not visible in the panel.
The pop-up in the webmap automatically sets these fields as an active link (if they start with https://).
The "end date" isn't visible either, which is a bit annoying for events over several days, and people cannot see the duration either (if it's on the same day).
Is there a way to make those fields available in the info panel if they are filled?
In the mean time I filed an idea for this: https://community.esri.com/t5/arcgis-indoors-ideas/customize-event-info-panel/idi-p/1397749