I have yet to try a Touch Bar in real life, but the concept of having a new interaction input with direct visual feedback on macOS sounded too exciting for me not to do something about it.
After I tried the Touch Bar simulator in Xcode I felt the brightness control would behave differently than it did, and then I tried to recreate what I imagined.
The prototype should work well on desktop and on the iPad.
If you tap the button it shows the progress bar, and you can drag the knob to wherever you want. But the next time you open the panel, the knob will always coincide with the current value in the progress bar, meaning that if you're at 0% brightness, you can only go to the right.
It may seem strange at first because we're not used to this type of behavior, but if you simply focus on your intent to slide the button to the left or right to get decreased or increased brightness, I think it feels natural.
I also created the whole keyboard and MacBook Pro in Framer. This was because I wanted to train drawing things using code and to get a bit more acquainted with classes, so it was the perfect situation.