For some reason I cannot add a map frame to a layout. I went back to ESRI training materials (Getting Started with ArcGIS Pro, 5 hrs 30 min, section Create Map Layouts), and still could not, although I had no trouble when I did the course. I've tried other data as well. Possibly relevant??:: I did fiddle around with Project>Options>General>Create Projects in the interim and don't know what the default settings are. Any thoughts?