Have you tried to create the form that you are passing information into via the custom URL within Survey123 Connect and leave out the "Geopoint" question itself? I have posted a few surveys to ArcGIS Online without a "geopoint" question and then I use the custom URL to pass information from a different form into this form.Then I turn around a pass additional information from this form into a completely new form for other data capture.
Survey123 Connect will automatically create the point feature class within the Hosted Feature Service(HFS) and this new point will be named exactly what the "form_id" contains under the settings tab. I would think that you would be able to use the coordinates from the previous form as the x= and y= portion of the custom URL; which should place a new location without the map present in the survey form. If this doesn't work, then do not tell the Survey123 team as it is working for me. 