Yesterday I tried to plug my FP4 in my car (Toyota Yaris 2009 with a jack input and NO bluetooth) and it DIDN’T worked 
My config: FP4 (stock OS) → Fairphone USB-C to jack adapter → jack-jack cable → My car jack input
When playing my podcast the sound goes out of the phone.
Strange thing is that the USB-C is in “charging only” mode (even if not charging), and no possibility to change that:
The USB connection is controlled by the connected device (Appareil connecté), and if I click to “This device” (Cet appareil) after a dozen of seconds it says “Failed”