Mac Keyboard Light at Login

I have a 2017 MacBook Pro running Big Sur. I travel a lot (pre-covid) and when I'm on a flight and it is dark it is really hard to type in my password at login because the keyboard isn't lit.

Is there a way to change the settings so that the keyboard is lit during login?

If you have FileVault enabled, the login screen at boot and hibernation resume is actually drawn by EFI, not macOS - macOS is not yet running at that point. Because EFI is a constrained environment, it does not include a driver for the keyboard illumination controller. So there is no way to light the keyboard until you've logged in and EFI continues on to load macOS, which does contain the driver you need.

You have two options:

1. Disable FileVault so that you boot directly into macOS (not recommended!).
2. Don't shut down your system and instead either put it to sleep shortly before your flight or change your hibernation delay via pmset (see man pmset for details) so that the system stays in S3 sleep and doesn't enter hibernation prior to the time you need to use it.