Here are my thoughts on the ProMotion displays (I have the MBP 16, and iPhone 13 Pro Max). While there is a noticeable difference compared to 60hz, it's not a great as it could be.
ProMotion is adaptive, meaning it can go up to 120hz; it’s not running at 120hz (for obvious reasons like battery life). However, I don’t believe we get full 120hz most of the time. If you guys ever get a chance, look at the screen of something like the Sony Xperia Pro, which enabled 120hz only mode. The motion is buttery smooth for anything you do on the phone. Yes it eats up battery life, but it’s smoother than the iPhones ProMotion adaptive display.
Same for the MBP. While I love the MBP screen with smoother scrolling than at 60hz, it could be smoother if we could lock in the full 120hz.
It would be great if we had an option to force 120hz somehow (like when it’s plugged in). This would unlock the full potential of the 120hz display.