As an alternative, I managed to get bluputdroid working on another phone to basically emulate a bluetooth keyboard/joypad - and yes, it connects to the pinephone and inputs are picked up by retroarch/games. Not a real substitute for hardware but it works!
retroarch_pinephone.jpg (Size: 73.77 KB / Downloads: 510)
bluputdroid.png (Size: 21.33 KB / Downloads: 485)
retroarch_pinephone.jpg (Size: 73.77 KB / Downloads: 510)
bluputdroid.png (Size: 21.33 KB / Downloads: 485)