Will the iPhone 12 5G network work in Vietnamese?

Hello guys

am planning to buy the iPhone 12 pro max from the USA through a friend

my question is:

I heard if I buy it from the USA then the 5G service won’t be working in Asia ( Vietnam to be specific) even if they have 5G service providers, ( due to The deference In the band width)

please advise me A S A P

before I buy the phone

best regards

Anwar S

[Edited by Moderator]