For new devices, Leawo iOSFix only supports downgrading from beta(if there is) to the latest official iOS version. No other downgrades are supported since Apple won’t provide system downgrade entries.
For devices before iPhone 7, Leawo iOSFix may provide 2 iOS system versions. You can downgrade the system if your system is already the latest iOS version that device ever supports.
This FAQ is about: Frequently Asked Questions, iOSFix, iOSFix for Mac