What are you using with your new Jolla phone to attach your 3.5mm headphones? My ideal solution would be that both usb-c and 3.5mm jack would available to use at the same time but I don’t know if it is possible?
For general discussion about 3.5mm missing in the new Jolla phone see the separate thread 3.5mm jack on new Jolla Phone.
What are you looking for beyond USB-C to 3.5mm jack adapters known to work with Sailfish OS?
Indeed, this thread is a duplicate. While it adds a constraint, that still fits in the other thread - and has in fact already been addressed there.
Combined cables:
Apologies, this is a duplicate. I’ve edited the title. Thank you.
I do not have the new Jolla, yet, but I have tested this adapter on a cheap Samsung smartphone and it works fine. I is not expensive and I see no reason why it would not work on the new Jolla:
Ugreen USB-C to 3.5mm Jack Adapter