Have you checked the list of compatible USB-C audio adapters?
I had a quick glance and couldn’t find one which specifies stereo line-in, most seem to support only regular mic-in, didn’t find P.MMIC / P.382 mentioned either, so most likely mono.
You should probably be looking for something like a Roland GO:MIXER PRO-X
That’s made for that kind of usecase. It supports Android, can’t tell you how well it works in conjunction with the FP4 though
