Update 2: the converter only works on my digital headphones. A pair that required analog input did not work. (While the apple one did)
Also note: the DAC disconnects randomly. Setting "Allow new USB devices" fixes this. (Why does GrapheneOS not remember the device?)
But the sound quality is perfect for me.
Devices tested: Pixel 6a
DAC Model: Hama 00200318 "USB-C Audio Adapter"
Result: complete garbage. The sound is completely distorted, especially the Bass. The build quality is also cheap, thick cable without fiber or anything, bad on the port.
The Seller (quote: "wholy fuck!") took it back immediately ;D