IPHONE 12 Pro Max comes with a SIM card inside

It would appear that you have purchased from an unauthorized dealer. Return the phone for a refund, then purchase from an authorized dealer.

It depends on what you have ordered?

• Unlocked SIM Free
• Locked to a Carrier with SIM

Did you order directly from Apple?

Do you live in the US?

Not necessarily. I bought mine from AT&T and it came with a sim card already installed. Of course, I already had AT&T as my service provider.

But, the original poster is not in the US, so there would be no reason for a US based cellular provider SIM to be in the phone.