I have not been able to find the maximum number of attribute fields allowed in an AGOL feature Service. Specifically, what is the max number of attribute fields for a related table in a feature service created using Survey123?
Currently the maximum number of attribute fields supported by Survey123 is 1024 for ArcGIS Online and 500 for Enterprise (Portal). This applies to the related tables (repeats) also.
This is documented here: Frequently asked questions—Survey123 for ArcGIS | ArcGIS
Retrieving data ...