Harrysntn! I found it! Go to Windows Update, mine said everything was up to date (because I had updated everything under the sun yesterday) but there's this little link that says View Optional Updates or some such. There were two -- I did the first one, no effect. The second one was Intel 27.20.100.9664. I installed that one -- it was a big one. The moment it was done, my screen immediately brightened. And my brightness buttons work! It says I need to restart for it to take effect but it's already fixed! (I will still restart).  
Hi, I'm currently using a Dell Inspiron 7501 with window 11. My brightness keys which are F6 and F7 are both not working. I can't even change my brightness in the setting of the device. Please help me!
Brightness keys not working for Dell Inspiron 7501 Window 11