On your DJIGO 4 App you will see a camera icon about midscreen on the right hand side with curved arrows above and below it. Should be a red circle around it to show which mode -photographic camera or video camera mode - you are in, and therefore which settings you will be affecting with your setting changes.That's the toggle you need to select FIRST when making camera settings changes on your Mavic.
Since you are wanting to change your video settings, toggle that on screen icon until the video camera icon is highlighted instead of the camera icon. That is the only way you will have access to adjusting the video settings of your Mavic. Conversely, if you wanted to make changes to your regular photographic camera settings, then toggle it until the camera icon is highlighted. Remember, your Mavic has to be powered up as this setting change directly affects the drone's software/hardware relationship. Again, this is where you WILL be able to select .MOV as your file format since that screen will now be accessible to you.
Give this a try and see if it all falls into place as it should. Don't hesitate to reach out again if you don't get the results you should now expect, and let us know if all is well when you get the chance. Good luck. But this should solve the slight hiccup you were having.