I thought I would update this in case anyone has a similar problem or sees the update and can contribute.
I got the usb c adapter working with AmpliTube, it’s a quite noisy and needs a noise gate to work but it’s useable.
Now I can set AmpliTube as my input device in GarageBand and it also works, if I switch back to the guitar direct input nothing but nasty feedback. This makes me think even more that this is a problem with how GarageBand handles inputs and microphones on the usb c iPad not a problem with the adapters themselves. It could probably be easily solved by having an input selector in GarageBand.