RandomMan25XX I have no function keys capable of adjusting brightness
this should work:
pomon sudo eopkg it budgie-brightness-controller-applet
install it, logout and login or reboot, open budgie desktop settings, go to panel, click "add applet" search for budgie brightness, select it and then click on "add". At this point should be good to go, click the icon of the applet on the desktop panel to start to use it.