When using Lightroom Mobile to shoot DNG on the iPhone 11 Pro Max, the model records as iPhone in the Model field. When using the iPhone camera it records properly as "iPhone 11 Pro Max." The EXIF fields cannot be changed using Lightroom Classic. It looks like this problem will have to solved with an update.
Since the iPhone 11 Pro Max has just been released, certain aspects of the images clicked with the phone are currently not fully supported. Our developers are working on including full support of the images from the phone and may include it in a future update.
I am looking forward to that update so that I can continue to use Lightroom Mobile. I switched to Halide until Adobe can get this done. Interesting that a small company like Halide has iPhone 11 Pro support immediately but a large and well funded (I’m a CC subscribers) is still sitting on the pot.