Differences in models.

The primary differences are slight differences in the bands supported by the cellular radio and the fact that the warranties are only valid in the country where originally sold.

Both were discontinued in September of 2022.

As far as Apple Article goes there is no Indian model as such. There is this Other country. I have been buying iPhones since 2009 from the USA and have been using them in India with Airtel, Vodaphone (Vi), Jio, and BSNL Carrier. My first iPhone was iPhone 3GS. Then 4S, 5, 6, 7, 8, and 12 Pro in the year 2021. I even bought iPhone 13 Pro last year for my daughter from the USA. There is no issue using them in India with any carrier even with 5G Airtel in Mumbai on both 12 Pro and 13 Pro.

iPhone 13 Pro Max

Year introduced: 2021

Capacity: 128 GB, 256 GB, 512 GB, 1 TB

Colors: Graphite, gold, silver, sierra blue, alpine green

Model numbers: A2484 (United States), A2641 (Canada, Japan, Mexico, Saudi Arabia), A2644 (China mainland, Hong Kong, Macao), A2645 (Armenia, Belarus, Kazakhstan, Kyrgyzstan, Russia), A2643 (other countries and regions)

As stated by KiltedTim,

IMPORTANT RESTRICTION FOR iPHONE, iPAD, APPLE TV, AND HOMEPOD SERVICE.

Apple may restrict warranty service for iPhone, iPad, Apple TV, and HomePod to the country where Apple or its Authorized Distributors originally sold the device.