I'm using a Lenovo Flex 15 with Ubuntu 18.04, and even when I move the brightness slider in the settings the brightness doesn't change. The Fn buttons don't work either. I tried the acpi_backlight=vendor
thing, and it still doesn't work. I use an NVIDIA GeForce MX230 graphics card. Even if there's a way to just force brightness change using the terminal, I would be open to any suggestions.
EDIT: Even brightness control has no effects. When I change the brightness using any method, my screen's actual brightness level stays the same even though the settings stay otherwise. And now the brightness slider has completely disappeared