Align Active Camera to View - Not working in 2.9 Align Active Camera to View
I used to do use this command all the time in 2.79. Now in 2.8 it's not working anymore - greyed out in the menu.

Why might this be?
For anyone who doesn't know - this operation is useful because you can use the Viewport to approximate what you want framed in the shot, then place the active Camera there (as a starting point before fine-tuning its position). I mean, was useful when it still worked.
Additional info - camera settings:
The camera was behaving like the Active Camera (possibly because it was the only one in the scene), but technically it was not the Active Camera.
Selecting the camera object and specifying this resolved the issue.