Can I use my iPhone for car audio without unlocking it?

Try enabling the media controls on the lock screen:

Access features from the iPhone Lock Screen - Apple Support

DMWallis wrote:

I'm using an old iPhone 12 Pro to play songs from my Apple Music library in my car using Apple Car Play. I leave the phone in the car except when I need to charge it or sync my music. I have the phone set up to use Car Play while the phone is locked. However, I still have to unlock the phone any time I need to enter the passcode, which is relatively frequent. (I don't drive the car every day.) I was using the iPhone without a passcode, and that works, but I'm concerned about security issues. I have all my music organized in Apple Music and have no interest in using a different music storage option.

What are my options? Maybe signing out of my Apple account and not using a passcode? None of my music requires authentication.

It's either you set or don't set a passcode.

Apple music requires you to log in, so signing out is not an option.

DMWallis wrote:

I guess I wasn't clear. "None of my music requires authentication." I use the Apple Music app only to play my own music, not to listen to music streaming. All my music is on the phone. My old phone plays music just fine when I'm not signed in.

Did you MISS the part about you either set or don't set the passcode?