How many people from the US migrate to Mexico?

The premise in your question appears to have an inaccuracy—in general, there is higher net migration from Mexico to the US compared to the other way around. According to 2020 estimates from the World Bank, there were approximately 1.02 million US citizens living in Mexico, while there were roughly 24.9 million individuals born in Mexico residing in the United States. Over the past decades, there has been a consistent pattern of Mexican immigrants moving to the US for economic and societal reasons.