Security settings are requiring passcode to old phone I no longer have

When restoring a new iPhone from a backup, the device may ask for the old passcode of your previous device or Mac to ensure the security and integrity of the backup data. This is part of Apple's security measures to protect your personal information and prevent unauthorized access to your iCloud backup.

Here's why this happens:

1. Encryption and Security: iPhone backups created using iCloud are encrypted to safeguard your data. The encryption is tied to the passcode of the device that was used to create the backup. When restoring a new iPhone from an iCloud backup, it needs to verify that you are the rightful owner of that backup. Asking for the old passcode helps confirm your identity and ensures that only authorized users can restore the backup.
2. Two-Factor Authentication: If you have enabled two-factor authentication on your Apple ID (which is recommended for enhanced security), the passcode verification process adds an extra layer of authentication. By confirming your old device or Mac's passcode, you demonstrate that you are the account holder and have access to the trusted devices associated with your Apple ID.
3. Preventing Unauthorized Access: Without this additional security step, it would be easier for someone else to restore your backup to their device if they somehow gained access to your iCloud account credentials. The passcode requirement helps prevent this scenario and ensures that your data remains private and secure.

When setting up your new iPhone and restoring from an iCloud backup, make sure to have the passcode of your old device or Mac handy. If you have forgotten the old passcode, you might encounter difficulties during the restoration process. In such cases, you may need to recover your Apple ID or use an iTunes backup that was created with a different password. It's always a good idea to keep your passcodes and Apple ID credentials in a safe place to avoid any potential issues during backups and device restores.

How did you remove the old phone? The right place is Settings/[your name]. At the bottom it will list all devices sharing your Apple ID.

This user has found a way --> iOS update - prompt for old passcode - Apple Community

The reasons I can think of is...

• If you are restoring from a backup that was taken from another device that had another Apple ID/Passcode, then to protect your data you are required to give the passcode of the other device too. This could be one reason.
• If you have changed the Passcode of the current device after erasing it and are trying to restore it from a backup that was taken using another Apple ID then also it may need the passcode that you had earlier.

The best would be to reset the passcode of the current device --> reset passcode -> If you forgot the passcode for your iPhone, iPad, or iPod touch, or your ... This would not ask you for the old passcode.

That is the best I can think of.

Set up your iPhone or iPad : Press and hold the device's power button until you see the Apple logo. You'll then see "Hello" in many languages. Follow the onscreen ...

Use a new Apple ID. Do not use an existing Apple ID...

How to create a new Apple ID: Create your Apple ID using the App Store on your device ... Tap Create New Apple ID. If you don't see this option, make sure that you're signed out of iCloud.

If you are the owner or the owner has shared all information with you then to open Activation Lock:- If it is Activation locked, read here --> Turn off Activation Lock - Apple Support Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Learn how to remove a device from a previous owner's account.