My iPhone 8 is no longer working after updating to 14.7

Someone jailbroke your iPhone to bypass the carrier lock on it. Now that you have updated you have removed this hack and the phone is now locked to a carrier. You will need to contact that carrier and ask what their unlock policy is and whether you qualify? Go to Settings > General > About > Carrier Lock to see who it is locked with.

How to unlock your iPhone for use with a different carrier - Apple Support

Can you do a forced restart? Force restart iPhone - Apple Support

Restart it.

So it was hacked not only to get around carrier lock buy also for Activation Lock? Or is that an Apple ID that you actually used once? And why do you have multiple ones.

Go here to recover your Apple ID: https://iforgot.apple.com/password/verify/appleid

Is that the full message or is it longer?

Click on the blue letters in my previous post. They are a link.

Then recycle that iPhone responsibly, without being able to recover the email and clear Activation Lock you will never be able to address your carrier lock.