I'm working with some folks at MapBox to display community science data we collect via Survey123. Rather than export the data to a file I'd have to send them periodically, we'd like to access the data via the REST API, or otherwise.
Every one working on this project is donating their time, and unfortunately none of us are familiar enough with the API to know the answer.
The data collected by Survey123 is stored in an underlying hosted feature layer in ArcGIS Online, which includes the capability to expose the data through a query operation in REST API for various kinds of format, including GeoJSON. For example: http://sampleserver6.arcgisonline.com/arcgis/rest/services/Wildfire/FeatureServer/0/query?where=1%3D... will return all features in the layer in GeoJSON format.