I have tried to change the screenbrightness in the settings but it hasn't worked. I also tried using the keyboards of the laptop. Then I tried to edit grub, which also didn't work. Does anyone know how to change the screen brightness?
You probably run kernel version 5.4 (which was the case for me). With a newer kernel it should work. I have the 4700U processor, whose internal graphics is apparently not supported by the older kernel's driver, with the new one adjusting the screen brightness via the fn button works.
According to this article (https://www.phoronix.com/scan.php?page=news_item&px=Ryzen-7-4700U-Daily-Driver) Version 5.7 should work, I used 5.9, and since I'm a noob installed it using following instructions: https://www.fosslinux.com/44138/linux-kernel-5-9-new-features-how-to-upgrade.htm