Error 4000 when trying to upgrade to iOS 14 on Apple SE (2nd Gen). I've tried all of the suggested fixes but still have the error.

See this --> If you see an error when you update or restore your iPhone ...

Or this --> iOS update and restore errors - Apple Support

Without knowing what “the suggested fixes” are it’s kind of hard to help. But here’s a couple you may have missed:

• Update over the air by going to Settings/General/Software Update
• Go to Settings/Touch ID & Passcode, enter your passcode, then turn off passcode, then updating using your computer.