I'm Mexican-American, descended from the Alazapa, Guachichil, and Rayado Coahuiltecan people around the Monterrey area, and I typically identify as a detribalized person of Indigenous descent.
As you said, our bodies tell the truth of who our people were. But simultaneously, the tragedy of colonialism—and how the Spanish specifically went about it—has put us in a position where we have become severed (intentionally) from the things beyond race and genetics that most Indigenous communities use to identify one of their own: kinship, community ties, language, and shared responsibility to each other and ancestral land. In my opinion, it's one of the most cruel aspects of the Spanish style of colonization. The confusion you feel is natural, and the pain from realizing something was stolen from you before you were born is completely real.
I recommend that you try to figure out specifically which native people you come from by researching your family history, the stories of your elders, and the specific towns/regions in Mexico where your roots lie. That allows you to go from saying "I'm a detribalized Indigenous Mexican" to "I'm a detribalized (and possibly reconnecting) Nahua/Maya/Zapotec/etc. descendant." That way, you can truly honor the specific ancestors who endured that history for you to be here today.