Hello,
From this blog post: https://www.esri.com/arcgis-blog/products/arcgis-online/mapping/introducing-related-record-editing-in-map-viewer/

I am expecting that I should be able to see related tables in form builder.
However when I open a Web Map item, I am not seeing a category for related records:

however when I open the same web map in Field Maps, I do see the related records as expected:

The map is pulling from a Feature Layer which is hosted on a standalone ArcGIS server. Is there anything I would need to do to enable the tables? Ultimately I would like to eventually create an Experience Builder app which allows users to create related records.