I'm new to GrapheneOS and still learning new things every day. Just wanted to put this one out there for the newbs.
I've got a Pixel 6a and it doesn't have a headphone jack. I ordered a cheap usb-c to 3.5mm connector figuring that it's impossible for that to not work..
When I got it, I tried it and it would never play through the headphones. I tried different headphones and all the same.
I ordered a different brand that specifically mentioned that it had dac figuring that this was the problem. Still no luck.
I went to Bestbuy and got the Google version.
Got home and tested it out and still didn't work.
Tried searching for this problem and didn't find any mentions.
Yesterday, I was going through the phone settings and I realized that as part of the privacy and security mantra, I had turned off USB access..
I have now changed that to allow USB when unlocked. Lo and behold, all these devices now work. Yay!
Hope this helps someone later on.