turn off Ken Burns effect

In the iMovie menu bar at the top of your screen, go to iMovie/Preferences and change the Photo Placement setting from Ken Burns to "Fit". Ken Burns will be removed from all clips added after you made the change.

For Ken Burns clips already in your timeline, select them and click on the crop icon (the one that looks like intersecting angles) in the tool bar at the top right of project screen. In the style option box that appears, choose "Fit" as the setting.

-- Rich