Fn+Tab is the backlight toggle on my V5 Max (and it's specifically called out in the user manual https://www.keychron.com/pages/keychron-v5-max-user-manual http

Fn+Tab is the backlight toggle on my V5 Max (and it's specifically called out in the user manual https://www.keychron.com/pages/keychron-v5-max-user-manual https://www.keychron.com/pages/keychron-v5-max-user-manual)