New iPhone is asking for security code to set it up but I can't find it

When signing into iCloud on a new device, you will be prompted for a two-factor authentication code that is sent to a Trusted Device that was used when you set up the Apple ID. This is normally called a Verification Code. If you no longer have the Trusted Device, you usually have the option to send the code to one of the Trusted Phone Numbers on your account.

Two-factor authentication for Apple ID - Apple Support

If you no longer have that device or a Trusted Phone number, you will need to attempt Account Recovery by going to this website and resetting the password:

https://iforgot.apple.com

The other code could be the optional security measure called a Recovery Key and would have been turned on when you had your account 5 years ago. This code is 28 characters is provides extra protection for your Apple ID. It is not used very often, because if you did not write this code down and no longer have access to the Trusted Device, then you would be locked out of your account permanently.

Set up a recovery key for your Apple ID - Apple Support

A screenshot of what you are seeing may be helpful to narrow down exactly what it is asking for.

Did you purchase a used iPhone from some person? If you did, read this link as you have more than likely been scammed --> https://discussions.apple.com/docs/DOC-250001038

Where did you buy the iPhone? A new iPhone doesn't have a passcode or a security code setup for a two factors authentication, it's new to setup following the instructions on the screen

Set a passcode on iPhone – Apple Support

You should return the phone as it is not a new device. It will most likely always be a paper weight.

What is the exact message you see on your iPhone screen?

If you’ve never used your Apple ID for 5 years, maybe you don’t have photos and files you want to keep, so why not set up a new Apple ID on your new iPhone ?