Apple will Unsigned IOS 13 soon. Currently not yet to Jailbreak IOS 14 so you can’t bypass icloud. You can use iFrpfile all in one tool to block update avoid idevice auto update OTA. 100% tested .
HOW TO DISABLE AUTOMATIC UPDATE ON IPHONE
What you need to do is open ifrpfile tools on your system and connect your phone to your pc and click on block ota pdate and Erase all contents then done….