Adaptive Brightness debuted in Android 9 Pie this year, and it is supposedly going to adapt to the lighting in the room that you are in, and work better than auto brightness. It uses machine learning to figure out how bright you want your screen in certain lighting conditions, which also conserves battery life, by not being overly bright when you don't want it to be, which is also pretty helpful. It has actually worked quite well, up until a few weeks ago. It would go pretty dim in darker rooms and then when you get outside, you could see the brightness going up til you can actually see the screen. So it does work, and work pretty decently, but as of lately, it hasn't worked at all.