It is apparent that different people prefer different brightness on screens and keyboards. I suggest that the same would also apply for the touch bar. I believe it would be useful to have the ability to control the brightness of the touch bar under control of the preferences and also be able to apply it programmatically as any other of the touch bar preferences. Also, maybe on a particular function. So, maybe more used functions would show up in the touch bar as brighter.
I also think this would be a great feature for BTT.
As a workaround, I created a custom Touch Bar configuration with my own buttons for which each has adjusted the colors to be darker. I use this configuration 99% of the time.
It was tedious to set up, but I'm happy with it for now.
What would have made it easier would be to have a global brightness setting for BTTs buttons at least.