Hello Legancy,
Welcome to Microsoft Community.
While I'm curious about how your cousin achieved all this, allow me to provide you with some official information.
In Microsoft's official support link, the Surface Pro 4 is indeed not listed as supported:
Which Surface devices can be upgraded to Windows 11? - Microsoft Support
Although your Surface Pro 4 device is equipped with an i7 CPU, please also make sure that the CPU is in the supported list:
Windows processor requirements Windows 11 supported Intel processors | Microsoft Learn
If you notice that your Surface Pro 4 device still doesn't meet the requirements of Windows 11, I think you'd better not take the risk of trying to update Windows 10 to Windows 11, as this could lead to irreversible errors.
The most direct way to determine whether a computer can upgrade to Windows 11 is to use PChealthcheck to check whether the computer meets the conditions:
Best Regards,
Mitchell | Microsoft Community Support Specialist