I drive a 25-year-old car and the only reason I'm able to play music from my phone on the car's sound system is that it was built to accommodate a 6-disc CD changer in the trunk. For $50 I was able to hook up an accessory that plugs into the changer port and fools the car stereo into thinking the audio signal from the phone is actually coming from a CD changer. Unfortunately my newest phone of course has no 3.5mm audio jack and the USB-C adapter has like a third the maximum volume of a normal plug. Oh well, better for my hearing at least.
I have found that different USB adapters will vary wildly in their max volume and sound quality. I bought a Google branded one from a local retail store and it kind of sucks. I ordered a higher end one and it gets louder and sounds better at high volume.