Google at least ships a dongle in the box, which will allow you to plug in your headphones. But you still can't charge and listen at the same time. Google has a compatible adapter in the Google Store that can do charging and listening, but it costs
$45. If (or when) you lose the packed-in dongle, a replacement is $9, which was
recently lowered from the MSRP of $20. If you're looking for an alternative USB-C to 3.5mm adapter, it needs to support "digital audio" as opposed to analog. The USB-IF has
specs for both modes, but the digital audio adapters actually need to have "multi-processing units" and amplifiers
in the adapter, hence the outrageous costs of these dongles.