I'm using an iPhone 13 Mini with iOS 18.3*. I went to Settings > Privacy & Security > Location Services > Compass, but didn't see the option to switch to from Magnetic North to True North.
I then did all four actions shown in the screenshot below: I reinstalled Compass, rebooted the phone, confirmed Location Services is turned on for the Compass app, and confirmed Compass Calibration is enabled. I also went to Settings > Cellular Data > Show All, and confirmed Compass was present and turned on.
Even with all that, there was still no True North option.
[*I'm on 18.3 because I just bought the phone, and that's what came on it. I did Erase All Content and Settings, but that doesn't affect the SSV. If needed I could attempt to do a full restore.....]
I then did all four actions shown in the screenshot below: I reinstalled Compass, rebooted the phone, confirmed Location Services is turned on for the Compass app, and confirmed Compass Calibration is enabled. I also went to Settings > Cellular Data > Show All, and confirmed Compass was present and turned on.
Even with all that, there was still no True North option.
[*I'm on 18.3 because I just bought the phone, and that's what came on it. I did Erase All Content and Settings, but that doesn't affect the SSV. If needed I could attempt to do a full restore.....]