My exp is iOS 14.x won't let you active your iPhone if you replaced some components before. I got an error when debug are :
AMDeviceCreateActivationInfoWithOptions failed (0xE8000013)
You can google this error code and try with some methods as well.
So if you replaced some components and upgraded your device to iOS 14.x you shouldn't reset your device at all. I trying some alternative to restore my device instead of iTunes or downgrade to iOS 13.x. Mine is an iPhone 6s that replaced the battery, it working well before I factory reset my device and it running the newest iOS 14.4. Can't active at all.
hleduc
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