iPhone 13 pro max mmwave why i dont have this anttena on side of my phone?

Models for the US market use mmWave. The additional antenna is of zero value in regions where that service is not available. You would need to contact your cellular provider to determine if they use that cellular band.

NOTE: models purchased in the US, will not have warranty coverage outside the US.

The models with the mm wave antenna are only sold in regions where that cellular service is available.