My only complaint is that the backlight behavior has like a dozen different settings, none of which are "off". There's "on", "flicker", "blink when you hit the key", "ripple out when you hit the key", "move in waves regardless of input", etc., but there's no "don't be light" option.
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)
It's fn+light-key on my keychron. Might work on yours.