The dynamic filtering of data in the table based upon the map extent is not currently possible within the survey123.arcgis.com website, however, you can accomplish this using ArcGIS Pro.
I will make note of your request in our backlog.
I am using custom templates and expecting the feature service to have quite a large number of records. At this point interacting with the map will be my best option. However, I believe implementing a filter by map extent will be highly valuable.