Apple has released iOS 12.1.2. According to the company’s notes, the update:
Fixes bugs with eSIM activation for the iPhone Xr, iPhone Xs, and iPhone Xs Max;
Addresses an issue that could affect cellular connectivity in Turkey for the iPhone Xr, iPhone Xs, and iPhone Xs Max.
You can download iOS 12.1.2 by going to Settings –> General –> Software Update.