The more usual thing are aux to USB adapters but they can only do USB to aux, nit the reverse. What you need is aux to USB converter, they can do both ways.

This article is good, autotranslate if not german.

https://www.amazon.co.uk/Kafuty-Mini-Transmitter-3-5mm-jack-default/dp/B084FYQD9S

I still have one. No these ones specifically don't have wireless capabilities. Later ones do, though.

Back in the day, I had one of the fm transmitters wired into the antenna with a ground loop isolator from radio shack (!) and I tapped a power lead so it would also charge my iPod while in use (and automatically turn off the power when the car was off). Honestly, it was awesome. CD quality sound. If I remember correctly Belkin made the transmitter.

I offered 3 potential solutions that work across ever model (unlisted) and you guys are downvoting?

• USB - apple 30 pin: note that the pin number might change depending on release year. Someone smarter than me will mention why firmware might not work out.
• USB to aux: this will give you a headphone jack and is the most reliable
• FM transmitter: if you lack a headphone jack you can also get an FM transmitter. It makes your device a mini radio station. These are pretty unreliable or staticy, but sometimes you need an option. I would recommend a new player first.