The 2021 14/16 inch MBP's don't have the Touch Bar nor the function keys dedicated to adjusting keyboard light. Has anyone figured out how to manually turn it off completely if I find it distracting?
You can do it from the Control Centre — the new icon in the menu bar that looks like two sliders. When you click on that, it shows a dropdown with several panes:
One of the small panes says ‘Keyboard Brightness’: click on that, and it shows a slider that you can drag from full brightness all the way down to none:
Note that in System Preferences, the ‘Keyboard’ tab of the ‘Keyboard’ pane has a few options related to the keyboard backlight that you might want to check: in particular, the backlight can be turned off after anything from 5 seconds to 5 minutes of inactivity.