We have a FieldParameters survey that was created from an existing feature service on Portal (behind the firewall). The survey is populating a related table only and has photo attachments. When I look at the data in Catalog I can see the FieldParameters table, the FieldParameters_ATTACH photos table, and the relationship class that was created by Survey123:
What has me concerned is that when I open the FieldParameters table in ArcMap, and then click on the "Related Tables" button, FieldParameters_ATTACH is not in the list. And it should be, since there's a relationship class. I have to create a relate on-the fly to check my photo attachments.