In the past, the iPhone would shoot from the telephoto in good light, but indoors or at night, it would crop into the main sensor. It's really easy to test. Cover a lens with your finger.

Switch to the video mode, select the telephoto, and then cover the telephoto lens with your finger. If it switches to the main camera, then you can assume it will do that at night too.

While in video, with the telephoto selected, then cover the main camera sensor. If you still see an image, then it's recording from the correct sensor.

iPhones are some of the only phones that should properly record 4K60 from all three rear cameras, but so far I believe only the Pixel 7 Pro can SWITCH between all three rear cameras while shooting 4K60 in one clip without having to stop recording to switch sensors.