This synchronization block occurs because your old iPhone's passcode acted as the unique decryption key for your end-to-end encrypted data—specifically saved passwords, Health data, and Home settings—and without it, iCloud cannot unlock or sync that information to your new device.
To fix this, you must force the system to delete the old, locked data by going to Settings > [Your Name] > iCloud > Passwords and Keychain, toggling the feature off and back on, and then selecting "Don't know iPhone Passcode?" followed by "Reset End-to-End Encrypted Data".
Alternatively, you can often find this reset option by tapping the "Finish Setting Up Your iPhone" banner in your main Settings menu. While this process will wipe your saved passwords and old Health data, it will not delete your photos, contacts, or notes, allowing your new phone to finally resume syncing with a clean slate.