I am not connected WiFi am using mobile data but not update

It appears that your iPhone needs to be connected to the Wi-Fi before you can update it. Using cellular data may not work as it is not as stable as the Wi-Fi network.

Please check this article for more info:

Update your iPhone, iPad, or iPod touch - Apple Support

It's also a good idea to create a backup of your iPhone first before updating it to avoid data loss:

How to back up your iPhone, iPad, and iPod touch - Apple Support

You may also want to connect the iPhone to the charger while updating.

Hope this helps! Best of luck!

If you want to update using Mobile Data you must at least have an iPhone 12 cq13 with a strong 5G connection.