Q: I've never run firmware 4.0.0 or higher on my switch, so my gamecard controller firmware is still not updated. How do i make sure my gamecard controller works after i downgrade back to < 4.0.0 ?
A: When flashing the firmware image for any 4.0.0 or later firmware, ChoiDujourNX will generate a protective hekate_ipl.ini on your microsd, with a "PreventGCUpdate" launch target. You must ALWAYS boot using this launch target (or add kip1patch=nogc to any launch target you wish to use in the future) and use a Hekate that supports the kip1patch option (releases here do:
https://github.com/rajkosto/hekate/releases) if you want to prevent use and updating of your GC controller firmware on firmware versions 4.0.0 and up.