You will use the Command Prompt to execute the downgrade.
Your iPhone 5s and a MFi-certified USB-A to Lightning cable. How to Downgrade iPhone 5S from iOS 12.5.7 to iOS 10.3.3! iphone 5s downgrade to 10.3.3 windows
Yes, it is possible and stable. LeetDown on Windows is more reliable than similar tools (like Vieux) because it doesn’t require a macOS VM. Just follow the DFU timing exactly, run as admin, and disable any antivirus. The iPhone 5s on 10.3.3 is still incredibly snappy and runs legacy 32/64-bit hybrid apps better than any newer iOS. You will use the Command Prompt to execute the downgrade
If you are reading this because you want to downgrade but you have saved SHSH2 blobs: run as admin
