Surface pro 3 Brightness control missing

I should add how I thought I shut off Automatic updates.   I turned off the options in the interfaces for Updates.   I went into services, and stopped the service(s).  Then I moved the update services (as an Administrator)  from either Auto or Manual to  "Disabled".   

I suspect most normal person would conclude that changing the configuration and disabling the Auto-Update Services would prevent updates.  

I can only conclude that one of the following is true:

1. My Surface applied some hotfix or roll-up (somehow, despite disabled auto-updates); OrT
2. There is one more auto-update setting I missed; or,
3. The bug is native to the older version and asserts itself at some point with 48 hours of a clean install to a particular old Win10 Version. 

I've already invested way too much time in trying to solve this issue, so I'm raising the white flag... and surrendering.  My surface will make a great docked Home Theater for one of our TV's (as an external monitor).

Yeah, I did wonder about that, whether it was reducing the power draw -- thanks for giving me a way to tell.  

But I don't often run my Surface all that long on battery power -- thanks to this problem, I've gotten in the habit of using my other laptop when I need a long time unplugged.  So this does at least allow me to use the surface in a dim room without blinding myself, which was the main thing I just couldn't cope with in this mess.

When I have more time and energy, I may turn back to working on the real problem, but I just can't waste any more time on this at the moment. So for now, I'll settle for this solution to the most pressing symptom (for me) and leave dealing with the underlying problem for another day.

https://github.com/sidneys/desktop-dimmer/releases/tag/v4.0.4

I am trying a temporary solution with this software This software may not display the speaker. But it can be controlled. We just don't see it.

My SP3 got the exactly same issues after updating to 1909. I've tried most of the solutions mentioned in this thread, and none of them worked. Resetting PC with keeping personal files was unsuccessful for unknown reason. 

Besides, I tried the "Surface Brightness Control" tool (https://docs.microsoft.com/en-us/surface/microsoft-surface-brightness-control), which is designed to "lower the overall carbon footprint" by auto dimming after some predefined inactivity period. Sometimes it can dim my screen to 20%, but most of the time it's not functioning. (I had to create the registry keys by myself, but it's still not working as expected after tuning the values.)

Finally, as suggested by this post: https://www.surfacetablethelp.com/2019/12/brightness-slider-control-missing-in-windows-10-on-surface-pro-3.html, I tried the third-party tool PangoBright. Win 10 is not mentioned on its induction page, but surprisingly, it works. It can adjust the brightness in 10% interval from 20% to 100%, which is good enough for me. (Seems it conflicts with "Surface Brightness Control", so that tool should be uninstalled.)

However, PangoBright is not perfect. The brightness still goes to 100% when showing the start screen and the side bars. And other problems (empty Power and Sleep setting, power button doesn't turn off screen) still exist. For now I have to live with this until Microsoft fix this stupid bug.

Update:

After using it for a while, I realize PangoBright doesn't change the screen brightness actually, but just change the color for all applications. So it cannot save any power consumption by LCD. 

In my last attempt, I managed to reinstall Win10 using the image downloaded here, which still allows me to keep my files. I don't know what happened, but after reinstallation everything looks normal: the version is 1909 and auto updating seems don't break anything.

I have found a solution for this now, though I don't know yet how permanent it will be. Anyway, this is what I did:

I firstly tried a Settings ... Recovery ... Reset this PC, keeping personal files. This failed after about 20 minutes with a rather unhelpful 'there is a problem'.

I then downloaded and ran the Surface Diagnostic Toolkit (SurfaceDiagnosticToolkit_SA.exe), available from the MS Surface support site. I allowed this to run, it takes about 15 minutes or so, but doesn't appear to do any good in itself, but it does reload the Surface Apps (perhaps one of these fixes the issue). In one of the last tests it sets the brightness to 0% then slowly increases it to 100%. In my case the brightness reduces to 0% OK but it doesn't increase after that. It then asks if I saw this brightness increase to which I reply No. The tool then exits.

I then ran the Settings ... Recovery ... Reset this PC again, choosing to keep my files again. This time it takes about 30 minutes but does go to completion.

When it finishes, the brightness and power settings work again as expected, and the update level is still at the latest (1909 as of Dec 19th 2019) version. I've run Update again to see if the fix is over-ridden, but it seems to be permanent, for the moment.

I've done this procedure on two Surface 3 Pros I have, with the identical problem, and the same procedure worked for both of them.

I hope this helps someone else.