I have recently started using ubuntu and my brightness controls on my keyboard are not working. The brightness control in the dropdown menu of ubuntu is also not working and the screen is too bright for reading. My laptop has a ryzen 3500u processor and a radeon vega 8 graphics card. The other answers regarding similar problems are all about intel graphics cards. Please help.
Install the Gnome Extension Adjust Brightness Icon
After installation and setting to ON you will find a lightbulb icon on the top bar.
Left click with the mouse to reduce the brightness to that required and keep clicking to reset to default. 4 clicks completes the cycle.
Don't forget that you can also set the Night Light ON with the right most menu drop down on the top bar.
The Night Light On utility helps considerably in reducing glare from over-white background screens.