I was able to get a working version of a dimmed screen. As the thread has mentioned, there is no way to actually dim the TV's screen. That makes sense and I totally get that, however, I wanted to see if adding an overlay could artificially dim the colors of my screensaver on the screen. The TV screen backlight stays the same brightness but after adding the overlay, I can see a noticeable effect "artificially".
By using the z-index, I added a new rectangle object to the screen, added a transition and size, with a color with an opacity level. Here are results:
Obviously, these pictures do not show the physical brightness of the screen but it did lower the apparent brightness of the white. Give it a try!