To turn off Live Photos, you have to turn the option "Settings > Camera > Preserve Settings: Live Photos" on.
Then turn Live Photos off in the Camera when you take the next photo, and then the Camera should be able to remember, that you turned Live Photos in the camera off. It is a bit strange, that we have to turn Preserve Settings: Live Photos" on in the Settings Camera, if we want Live Photos disabled, but it is the only way to make the Camera remember our last setting for "Live Photos".
See: Save camera settings on iPhone - Apple Support