It looks like
@GaryOderNichts and/or
@Maschell are my only hope when it comes to getting HID support in Retroarch.
The Retroarch github is massively busy with all the other systems when it comes to reporting issues.
I've managed to get HIDtoVPAD to work perfectly, creating a config.ini for a joystick I built with my own fair hands back in 2009 or so. But that is unable to run concurrently with Retroarch due to the way homebrew manages the Wii U memory. The HIDtoVPAD github had a discussion about it back in 2017,
https://github.com/Maschell/hid_to_vpad/issues/43 and it seems the 2017 version of REtroarch had HID support that worked!
But that has regressed and isn't the case now.
I also have Bloopair installed, that also works perfectly with my 8BitDo pad and because it loads into the memory of the Wii U in a different way it continues to work once I've booted into Retroarch!
It's like i'm stuck in the middle of two beautiful rocks of the homebrew scene! i need them to come together, or have a bridge build between them so I can have the best of both worlds.
A HID driver in Tiramisu that doesn't drop out memory on homebrew boot!