99% of those adapters are garbage that break down in month or so.
I am writing this on FP4 but I am also salty audio engineer and I would honestly trade my phones cameras to aux jack, just to avoid hastle.
It's an alt mode for USBC. But I've only ever seen HTC use it.
Most just expect you use a dongle with a DAC, but I prefer this way because the dacs in phones aren't always the best.