Thank you for the tips.
It would save significate time to be able to design for the mobile first and have it automatically scale up to larger screen sizes. The layout could then be adjusted, for a horizontal viewing experience.
Currently I have to go in custom mobile layout mode, configure the widgets, and then, manually add the widgets from the pending list for tablet and desktop. I never include anything that will not fit on a mobile layout, those widgets will always be moved to a separate page or excluded.
Option for Mobile editing first - Esri Community