The earlier post suggested microsoft drivers not Intel.....
Just posting in case others have this issue and are not using teamviewer.
That's interesting and definitely useful. In my case, I had also uninstalled the Intel graphics card device and drivers (provided by Intel, part of the Microsoft Surface pack), but that didn't fix the problem. I think all the MS Surface laptops have Intel graphics cards.
It seems that either or both Intel drivers and other screen management apps cause this control to disappear. People may have to fix one or both to resolve the issue.
For the benefit of others: Do you have or use any other remote control software, or perhaps the Intel "Wi-Di" or equivalent screen casting.
It might be that the common denominator is an app or drivers affecting or controlling screen settings, and only certain changes that break it.
In the Teamviewer case, the Brightness control disappeared when I used the software setting to black out the remote laptop screen. It had been in use as installed for 3 years, without causing trouble before that change.
I don’t use any screen casting software on my surface pro 3.
Also I’d like to add, the Intel driver directly from Intel might be more up-to-date than what Microsoft is providing since it’s dated as of March 2020.
Your issue makes sense though on why reinstalling teamviewer would resolve the screen brightness. Correct me if I’m wrong but that blackout feature requires a driver from teamviewer to be installed, right? That may be what caused it as you suggested but strange that it happened after 3 years.
In my case microsoft firmware updates caused the issue and I had looked into solutions about a year ago and could not get it working even after installing all the updates from Microsoft along with their driver package. I finally had some time today since I’m currently recovering from surgery and found a post on reddit suggesting to install the display driver from Intel’s site. This resolved it for me right away.