I have exactly the same problem. A surface 3 pro that has just had a Windows 1909 update. Exactly the same symptoms as the post with screenshots above.
ie - no brightness adjustment on Settings page, no option to choose adaptive brightness, brightness slider on Action bar is disabled, power options are all blank (so can't choose anything eg time to turn screen off on battery etc).
I tried restoring Windows but it just thought for about half an hour then said there was an error and it couldn't restore Windows.
I did provide Feedback on the Settings page with screenshots similar to the above, but I have no idea if it gets looked at or will end up at the right place.
Steve