The latest SEP/BB as of right now is iOS 15.1, and is partially or fully compatible with iOS 14 depending on your device. See the appropriate section for exact compatibility info.
- SHSH blobs for the version you want to downgrade to (e.g. from https://tsssaver.1conan.com/, https://shsh.host/)
- macOS (High Sierra has Problems with pwndfu) or Linux (Ubuntu 16.04 recommended). Windows or a VM will NOT work.
- If the exploit fails even after multiple attempts or your device reboots out of DFU mode, you'll have to start over from the beginning and be quicker next time. (You don't have to redownload anything though.) You may have to force restart your device if it's stuck in DFU.