This sounds like you have a messed up keyboard. Did you have a liquid spill at some point?
Just in case you don’t know here’s the user guide info on the Fn keys:
When you use the brightness control buttons you should see a icon on your screen which visually shows you the level.
@mercutio999 - Its not! The control via the Fn keys maybe they aren’t working.
Lets backup here... You are seeing the controls them selves both on the Screen and Prefs for setting? So its not seeing the control its the fact the screen is not altering, then the backlight logic has a problem!
Your Displays control panel also has a slider which you can use to adjust the screen brightness. Do you even see the control?
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Any news regarding the missing brightness slider?
crwdns2934271:0crwdnd2934271:0 Dave Menkehorst crwdne2934271:0
@Dave Menkehorst - By chance did you disable the discreet GPU as it had failed?
crwdns2934271:0crwdnd2934271:0 Dan crwdne2934271:0