This article is for you if you’re one of the many unlucky laptop owners who are faced with unbearable delays while changing screen brightness (it can take several seconds for screen brightness to change after pressing the function key responsible for changing brightness).
I wasn’t able to locate the source of this problem, nor fix it with any available online resources, of which there are many (e.g. here, here, or here). Thus, to avoid further frustration, I decided to use
xbacklight (which works without any delays) and assign it to a different key combination.