If Windows 10 made it so your backlit keyboard settings can’t be cycled through with the function key, go into your BIOS settings and manually change the keyboard light setting to whatever you prefer. I just suffered two days without my laptop’s beautifully backlit keyboard, and I assure you had I known I wouldn’t be able to turn it on, I would never have disabled it the night before “upgrading.”
But yeah, simple as that, just go into the BIOS settings. Simple. So easy of a solution anyone could think of it without taking multiple hours to try anything else first.