Hello Rkpro,
Thank you for using the Apple Support Communities! You have some questions about using Night Mode on iPhone 11 Pro. I can help.
Night Mode requires the iPhone to be held still to allow more light to pass through the shutter, so it would not be an available option during video recording.
When it comes to using Night Mode, it may not be available for every capture, as the cameras and iOS will automatically detect low-light situations, and determine if it can be used, which also depends on the camera mode you are using.
It sounds like what you are experiencing is expected behavior. You can learn more about the camera features on iPhone 11 and iPhone 11 Pro here: iPhone 11 and iPhone 11 Pro camera features - Apple Support.
You can also learn more about editing your captures here: Take and edit photos with your iPhone, iPad, and iPod touch - Apple Support.
Thank you for your post.
Take care.