https://doc.arcgis.com/en/field-maps/latest/prepare-maps/high-accuracy-data-collection.htm
Supported GPS metadata
If using a single GPS location to set a point's location, the following GPS metadata values are recorded:
- Receiver name
- Latitude—Position received from the GPS receiver before applying data transformations in the location profile
- Longitude—Position received from the GPS receiver before applying data transformations in the location profile
- Altitude—Ellipsoidal height received from the GPS receiver (not orthometric height, as used for z-values)
This would indicate the Lat/Long values stored in the metadata are in whatever datum you have configured your GNSS device to output in!
The geometry of the points is controlled by the map/layer's datum in AGOL, and is affected by whichever transformation you have configured in your Field Maps profile to display your GNSS data on the map. If you are using ESRI basemaps, the map will be WGS84 web aux. Unless you are publishing hosted feature layers to AGOL directly through Pro, your point layer is likely also WGS84 web aux. (you can verify the datum in AGOL, by links in the lower right corner of the layer's item description page)
It is vital to configure and document your GNSS device's output datum (if real time corrections are in use it's the datum the corrections are provided in!), and then carefully configure your Field Maps profile so the GPS output gets correctly transformed to the spatial reference of your map. From there the point geometry is either the map's or the layer's (I haven't had to test that yet because my maps and layers always match spatial reference)
Hope this helps, definitely the kind of stuff that keeps one up at night! 😄
