Hello Jason,
If this was an app that was on the iPhone 12, then it would make sense for it to download onto your new iPhone 14 when transferring the data.
Is it an app that you recognize from your old iPhone 12? Do you recognize the email?
We are not exactly sure what you mean by "a transferred app".
If the app was downloaded on the iPhone using that email and password, it would be normal to be asked for it again on the new iPhone.
We would go ahead and delete the app. If it is an app you use, then download it again using your Apple ID and password.
If you are concerned about the security of your account, you can check to see if anyone else has access to your device or accounts using these steps from See who has access to your iPhone or iPad - Apple Support:
1. Check which devices are signed in to your account by going to Settings
> [your name]. If you see a device you don’t recognize, tap on that device name and select “Remove from Account.”
2. Check to see if there is an unexpected alternate Face ID appearance or additional Touch ID fingerprint set up on your device by following these instructions: Set up Face ID and Set up Touch ID on your iPhone or iPad.
3. Sign in to the Apple ID website (https://appleid.apple.com) and review all the personal and security information in your account to see if there is any information that someone else has added.
4. If you have two-factor authentication turned on, review trusted devices for any devices that you don’t recognize. If you don’t have it turned on, you can turn it on by following these instructions: Set up two-factor authentication on your iPhone, iPad, or iPod touch.
5. Review the installed apps on your device and look for apps you don’t recognize or don’t remember installing. You can look up any apps you find in the App Store to see what their purpose is.
6. Mobile device management (MDM) configuration profiles—typically installed by employers, schools, or other official organizations—allow additional privileges and access to a user’s devices. To look for an unknown MDM configuration profile on your devices, see Delete unknown configuration profiles from your iPhone, iPad, or iPod touch.
7. To see if anything has been changed or added to your sharing permissions, see the checklist How to stop sharing your iPhone or iPad content.
Have a good day.