Problem: You updated your Ubuntu and the background button is not working on your Dell Laptop but you have work to do.
Solution: Fix it. Follow these steps.
Note: (Change the Red Text to your preference)

First…

1. Open a Terminal and enter the following for minimal brightness.

echo 200 | sudo tee /sys/class/backlight/intel_backlight/brightness

2. Open a Terminal and enter the following for maximum brightness.

echo 4648 | sudo tee /sys/class/backlight/intel_backlight/brightness

3. Note: You can set a range (Red Text) from 200 to 4648 to your preference.
Congratulations! You can see the screen!

Wait for an update or patch!