brightnessctl is a utility that can be used to control screen brightness in Linux, and it can be used with i3 window manager. To use brightnessctl with i3, you’ll first need to install the brightnessctl package from your Linux distribution’s package manager.
Once you have brightnessctl installed, you can use it to set the screen brightness in i3 by binding it to a keyboard shortcut. For example, you can add the following lines to your i3 configuration file (~/.config/i3/config) to bind the XF86MonBrightnessUp and XF86MonBrightnessDown keys to increase and decrease screen brightness, respectively:
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bindsym XF86MonBrightnessUp exec "brightnessctl set +10%"
bindsym XF86MonBrightnessDown exec "brightnessctl set 10%-"
In this example, the brightnessctl command is used to adjust the screen brightness. The set option is used to set the brightness level by a specified amount, in this case, +10% or -10%. You can adjust the amount by which the brightness changes to your preference.
After adding these lines to your i3 configuration file, save the file and restart i3 (by pressing Mod+Shift+r, where Mod is the key you’ve configured as the i3 modifier key) for the changes to take effect.