Hello,
I am trying to create a Workforce project. In the App Integration window, if I click on the Field Maps app to add maps to the project, only certain maps show as options to add. I don't know what the criteria are for showing those certain maps. The sharing is varied from just me to organization or groups for them but doesn't seem to matter. This has also happened when trying to add a feature service to Survey 123, so the issue might be the same for both. All the maps are created with feature services from our REST services on our server.
I was running into this issue (my maps weren't coming up in the list for the Integrate Field maps dialog). In my case, it wasn't about the sharing, but rather the map/layer settings. When you are configuring your form for field maps, you need to use the option "save to layer" rather than "save to map" in the upper right: