If you have a signed IPSW file and want to install it manually: iPhone 8 (GSM) IPSW Download - iClarified
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)
If you need the file for archival or advanced research purposes, you can find it on community-driven sites: Go to the iPhone 8 (GSM) page on IPSW.me . Identifier: Ensure you choose iPhone10,4 (the GSM model). Build Number: The specific build for iOS 12.1 is 16B92 . 🛠️ Official Installation Method (Latest Available) If you have a signed IPSW file and
Apple uses a "signing" system to control which iOS versions can be installed. iOS 12.1 is currently unsigned. Download iOS 12.1 for iPhone 8 (GSM)