That’s what I thought, Mexico City. Close but no cigar.
It’s Sao Paulo.
"São Paulo has a population of 21,650,000 people. Close behind is Mexico City with 21,581,000, then New York with 18,819,000, and Bueno Aires with 14,967,000.
Sao Paulo covers an area of approximately 587 square miles and has a population of at least 12 million people in the city and more than 21 million in the metropolitan area.
The Brazilian megacity is the country’s financial and economic hub, contributing significantly to Brazil’s gross domestic product. São Paulo is home to many national and international companies from a variety of sectors.
São Paulo is renowned for its abundant cultural diversity, stemming from successive waves of immigration. Over the course of its history, the city has drawn immigrants from numerous regions worldwide, such as Italy, Portugal, Japan, Lebanon, and various other countries. This cultural mosaic is vividly reflected in São Paulo's culinary delights, architectural styles, and cherished customs and practices."