iPhone 12 SIM Card?

It will work using 1 physical SIM card + 1 eSIM.

Start here:--> Using Dual SIM with an eSIM - Apple Support

Unless your model was manufactured for Chinese, HongKong or Macao markets. Should be this case, read this:--> Using Dual SIM with two nano-SIM cards - Apple Support

Regards

Giulio

Where did you buy this device from?

Here are a few of the many ways you can use Dual SIM:

• Use one number for business and another number for personal calls.
• Add a local data plan when you travel outside of the country or region.
• Have separate voice and data plans.

With iOS 13 and later, both of your phone numbers can make and receive voice and FaceTime calls and send and receive messages using iMessage, SMS, and MMS.2 Your iPhone can use one cellular data network at a time.

1. eSIM on iPhone is not offered in China mainland. In Hong Kong and Macao, iPhone 12 mini, iPhone SE (2nd generation), and iPhone XS feature eSIM. Learn about using Dual SIM with two nano-SIM cards in China mainland, Hong Kong, and Macao.
2. This uses Dual SIM Dual Standby (DSDS) technology, which means that both SIMs can make and receive calls.