DoubleTake by FiLMiC Pro captures multiple iPhone camera footage simultaneously
apps.apple.com
2 threads
I thought they were going to support recording all cameras at once (IIRC that was demoed at the iPhone 11 launch).
From what I can glean of this Verge article [0], it seems two cameras is the maximum possible at this time.
[0] https://www.theverge.com/2020/1/28/21083583/filmic-doubletak...
I take no ownership of this but found it an insanely cool free app that shoots a single video with multiple cameras.