Folks, I found an explanation in the Mac help believe it or not. The security warnings are built-in and can't be bypassed with a setting. You have these choices it seems:
1. Compose the pptx file with links on the Mac, then it runs normally. Copying files over from a PC produces the problem. 2. Run the presentation from OneDrive (didn't try that). 3. Run the presentation from user/Library/Containers/com.Microsoft.Powerpoint/Data/Documents/... I used the last option and everything is fine. Something special about that folder, but it's not obvious what it is. *Greg K* >
