I’m seeing numerous reports that iOS 12 beta 2 restores auto brightness function for affected phones, with True Tone still being disabled. One or two further reports state that a DFU restore to iOS 11.4 enables True Tone. I haven’t had a chance to test any of this yet. It does seem like Apple is working on the problem, although it remains to be seen whether any potential fix makes it into the final release. Stay tuned!