Can I use Lightning 3,5 mm converter adapter + random aux cable to connect to my car aux?

Hello Ege258,

Thank you for reaching out for support in regards to your questions about compatible adapters for your iPhone XR and an AUX cord.

Yes, that exactly correct and the idea for that adapter.

You can take a look at iPhone Accessories to select the Lightning to 3.5 mm Headphone Jack Adapter.

"The Lightning to 3.5 mm Headphone Jack Adapter lets you connect 3.5 mm headphones and other audio devices to an iPhone, iPad, or iPod touch that has a Lightning connector. Your iOS device also needs iOS 10 or later.

Plug your Lightning to 3.5 mm Headphone Jack Adapter into the Lightning connector on your iOS device and plug the other end into your headphones."

We appreciate you reaching out to Apple Support Communities. Be well!