Since iOS 12.1 is blocked, you should install the latest supported version for the , which is . Over-the-Air (Easiest) Open Settings > General . Tap Software Update . Select Download and Install . Using a Computer (Manual IPSW)
You cannot downgrade from a newer version (like iOS 16) to 12.1. 📥 How to Download (Archive Only) Download iOS 12.1 for iPhone 8 (GSM)
Apple uses a "signing" system to control which iOS versions can be installed. iOS 12.1 is currently unsigned. Since iOS 12
iTunes or Finder will block the installation of unsigned firmware. Since iOS 12.1 is blocked