One step you could try is to reset the network settings on your iPhone. Sometimes, network-related settings can become corrupted or misconfigured, leading to connectivity issues with Bluetooth devices. To reset network settings, go to Settings > General > Reset > Reset Network Settings. Keep in mind that this will reset all network-related settings, including Wi-Fi networks and passwords, so you'll need to reconnect to your Wi-Fi network afterward.
If resetting the network settings doesn't resolve the Bluetooth connectivity issues, you could try forgetting the Bluetooth connection to your car and then re-pairing it. To do this, go to Settings > Bluetooth on your iPhone, find the entry for your car's Bluetooth system, tap the "i" icon next to it, and select "Forget This Device." Then, follow the instructions provided by your car's manufacturer to re-pair your iPhone with the car's Bluetooth system.
If the issue persists even after resetting network settings and re-pairing your iPhone with your car's Bluetooth system, it's possible that there may be a bug or compatibility issue with iOS 17 and your car's Bluetooth system. In this case, you may want to consider contacting Official Apple Support for further assistance or visiting an Apple Store for hands-on help. They can provide more specialized troubleshooting and potentially offer a solution tailored to your specific situation.