I bought a new Lenovo thinkpad laptop. It's brightness was too high. When I tried to reduce it's btightness, the seekbar (a bar where you slide to adjust brightness) was working but brightness was not changing. I also tried using keyboard's fn keys but that also didn't work. So, here is what I did to fix that problem.

I looked at 'device manager' > 'display adapter' there was something called 'microsoft basic display adapter' which  was working properly and that was enabled too.

So I clicked on 'microsoft basic display adapter' clicked on 'driver' and clicked on 'update'. That gave me two option. I chose first one, which was to search update over the internet. And damn, I got update. I installed update and after successful installation, 'microsoft basic display adapter' became 'intel (R) UHD Graphics 620' and now I can control brightness.

Thank you.