With the iPhone 11, iPhone 11 Pro, and iPhone 11 Pro Max, Apple changed the way the Camera app’s shutter button works in ways that could cause confusion. Tapping it once still takes a single still photo, but if you press and hold on the shutter button, it now captures a quick video. (Previously, pressing and holding on the button took photos in burst mode; to do that on the iPhone 11 models, slide the shutter button to the left.) Once you’ve started taking a quick video, slide your finger to the right to lock recording, so you don’t have to keep holding the button down. Tap the white shutter button to take a still image while recording; tap the red record button to stop recording. For even easier quick video recording, press and hold either of the volume buttons; a single press still takes a photo.
Note that these quick videos always record with monaural sound and at a resolution of 1920-by-1440 (close to 1080p); for stereo sound and the resolution set in the Settings app > Camera, use the Camera app’s Video mode. So this quick video option is great if you have your default set to a higher quality but just want to take a quick and easy video that doesn’t consume as much storage.
Personally, I prefer to record in 4K at 24fps. The lower frame rate gives you a more cinematic look, allows your camera to capture lower light more easily, and also consumes considerably less storage than 30 or 60fps.