Hello David Hughell,
Since Geoshape and Geotrace questions don't use your device's location to fill in your response (other than to center you on the map), if you don't have an offline map associated with the survey you will see the little slash through the box to open the map.
Please use this link for reference regarding the Geotrace and geoshape question types: Geotrace and geoshape—Survey123 for ArcGIS | Documentation
In my testing, I had placed a small tile package in the media folder of the survey before publishing it. When testing with my device on airplane mode I was able to capture geoshape questions using the tile package as my basemap.
Please use this link for reference regarding using offline basemaps in ArcGIS Survey123: Prepare basemaps for offline use—Survey123 for ArcGIS | Documentation