how do I know if I have a SIM card

You couldn't have had it for that long, the 14 pro max only came out 10 months ago.

•iPhones sold in the US. do not have SIM card slots.

•iPhones sold in China, Hong Kong, & Macau have two SIM card slots, no eSIMs.

•iPhones sold in the rest of the world have one SIM card slot and one eSIM.

See if this information helps -

If you see 'invalid SIM' or 'no SIM' on your iPhone or iPad - Apple Support

barbp66 Said:

"how do I know if I have a SIM card: my phone says NO SIM .. it's a 14 pro max . i've had it for a very long time"

-------

Troubleshooting "No SIM":

A. Go Here: If you See 'invalid SIM' or 'no SIM' on your iPhone or iPad - Apple Support

B. Contact your Carrier:

Something went wrong with the SIM card's configuration. So, contact your Carrier, as they are the one who configures it. Getting this can occur for a number of reasons, such as installing a new update.