1. InDesign 16.1
2. In a document, select an object. Then hold shift and scale the object. Or hold option and drag to copy the object.
3. When holding shift, I expect constrained proportions. When holding Option, I expect a copy.
4. Both key modifiers work perfectly in Illustrator, so it's not my keyboard nor my Mac. What I get when holding shift is the same as not holding shift - unconstrained proportions. What I get when holding option is the same as with not holding option - the object is just moved, not copied.
5. I can't show a test because I can't show you when the shift or option key is pressed.

I should clarify the intermittent part of my title. It seems that if I keep at it long enough, keep option-dragging, or shift-scaling, at some point InDesign wakes up and the key combination kicks in. But that's crazy. This is still a productivity killer. Please fix!