Hello, this is Emily.
Keyboard backlight is actually not a Windows feature but a firmware feature. It is not one related to driver either, so reinstalling driver is not going to help either.
I will suggest that you reinstalled Vantage app and see if that helps. If not, see if you can find the feature in BIOS and make sure it is not disabled. If it is still not working, it is best you contact Lenovo as it can be a hardware issue hhere.