iPhone xs max not working in Pakistan

The error message indicates that your phone is carrier locked. You will need to contact that carrier to get it unlocked. As noted, which carrier was used in the US?

Was your phone previously locked to a different carrier?

Who was your carrier in the US? It's probably locked to them.

Are you getting any error messages, if so what do they say?

Then answer my question. Who was your carrier in the US?