FiLMiC Pro is one of the best video camera apps for the iPhone & iPad, and they recently released a new app called DoubleTake which allows you to take advantage of multi-cam recording allowing you to record on two cameras on your phone at the same time.
If you have the iPhone 11 Pro, then you are able to use two of the four available cameras, which include the selfie camera. This could be great for recording yourself while shooting a scene or have close and wide shots of the same subject.
Best of all, it’s free!