When creating Web Maps I always use the (new) Map Viewer. These maps are then used to configure forms in Field Maps. However when I edit the forms in Field Maps and then go on to make changes to my Web Map it gives me the following message:

That's why I started wondering why it saves my maps in Map Viewer Classic style. My primary map viewer settings are set to Map Viewer.
Does anyone know why? And perhaps how I can change this?
- Zoë