iPad mini (5th generation, Wi-fi model) downgrade to iOS 14.2

I want to downgrade iPad mini to iOS 14.2 from iOS 14.3 or later versions. Could you tell me how to downgrade?

I've already tried the following steps.

1. Download the ipsw file from: https://ipsw.me/product/iPad
2. Select downloaded files from Mac to iPad mini, press the "Restore iPad" button and "option" key.
3. Enter passcode on iPad mini.
4. Error message displayed.