I have the iPhone XS Max running iOS 13.1.3. I just tried using the camera in Lightroom Mobile yesterday for the first time because I want to use the RAW camera function. When I tried activating the flash it is greyed out and I cant activate it. When I switch to JPG the flash becomes white and i can access flash options. Please fix!
This happens every year when new phones come out, until Adobe is able to release a fix that works with the new phones. Until then, there isn't much you can do. By the way, in prior years/models, the issue was Apple related (as it was the same for other apps like Camera+ that also could not access the flash when capturing raw images).