I just helped someone who used Survey123 in Connect (v. 3.13.239) for a master thesis. The basemap was changed to OSM as default. When filling out the form, the basemap was OSM when using a web browser on a Windows PC, but unfortunately was Esri Topo when using the web browser on a smartphone (Android and Iphone). Why does the smartphone browser not show the set basemap (OSM)?
This are some old related posts from previous versions:
The workaround I used was to change the basmap of the Survey Map Form in ArcGIS Online after creating the Survey, because when filling out the Survey123 on a Smartphone it uses the created Survey Web Map as default Basemap.