I figured it out. It was all caused by images wider than they are tall but me specifying the image to be square

I added some color tracking and I can see that this extra space seems to be some kind of frame around the ScrollView. I guess I might have to explicitly set the height of the scrollview and not rely on it basing its height specifically on the contained content? Does swift UI have the concept of "wrap_content" for the height of a containing control?

Thanks. I was able to divide and conquer (again) and get the compiler unstuck. Dividing up the work is helping. Hopefully I won't encounter that agin if I keep subdividing my views