Issues with brightness control on i3wm ( in built keys shortcuts )

General system Kernel, boot, graphics & hardware
2

Try this:

bindsym XF86MonBrightnessUp exec brightnessctl -c backlight set +5%
bindsym XF86MonBrightnessDown exec brightnessctl -c backlight set 5%-

Brightnessctl is in extra.

Other options are light & xorg-xbacklight which off course have their own syntax. The problem with these keys is they are hardwired in the bios, so you might not get anything to work.