Why I can't put two SIM card in a new iPhone 12 Pro? Both are nano cards.

No, also for all iPhone 11 models and iPhone X series.

Phones intended for sale in China take 2 physical SIM cards, phones for anywhere else in the world take 1 physical SIM and 1 e-SIM.

It is not possible to put 2 SIM cards in a non-China phone.

the sim card tray must it be different? or is sim card especial? i have iphone buy in USA for default only have 1 sim card if i buy a new sim card tray for dual sim is working my iphone with 2 nano sim?

where i buy a dual sim card tray??

Your phone supports one nano sim an one esim

Is the capability for two different SIMs (i.e., 1SIM + 1eSIM) only for iPhone 12?