Unable to restore or update my iPhone 13

See this article.

If you can't update or restore your iPhone or iPod touch - Apple Support

"Unable to restore or update my iPhone 13: [...]I have an iPhone 13 with iOS 18.3 and forgot the Passcode to update to 18.4. Following the guidance I entered several Passcodes until it said Unavailable I have an iPhone 13 with iOS 18.3 and forgot the Passcode to update to 18.4. Following the guidance I entered several Passcodes until it said Unavailable"

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Troubleshooting a Locked iPhone:

"Unavailable" indicates that your iPhone is locked. So, get this serviced.

So, Being Locked Out...

Enter the passcode incorrectly too many times, and you'd likely be locked out for good. So, hold it right there, and refer to this link: If you Forgot the Passcode on your iPhone, or your iPhone is Disabled - Apple Support. It would be the one you've always entered. If you do not know it, then look for it in a location you may have stored it in.

No Success?

Contact Apple support:

If you cannot get the above link to work, then contact Apple Support.

Apple Contact Info:

• Contact Us - Choose Locations
• Proceed from there, as necessary

As for Updating an iPhone:

You can update your model a computer, and you can do so using Cellular, given you have the services to do so. Use my User Tips:

• Update your iPhone Using a Computer - User Tip
• Use an iPhone 12 or later, that is using 5G, in order to update over Cellular -User Tip