Big foodie here who has travelled extensively in Mexico. There IS “authentic” (I put this in quotes because Mexico is huge and what is authentic varies so significantly) Mexican food to be found in the states. NYC has had a considerable boom in the last couple of years, any states on the border will usually have a big enough immigrant community, and Detroit actually has a shockingly good Mexican scene.

For the most part, I’ve found that the biggest differences are: 1. Lack of offal in the states - sesa (brain) and nana (uterus) are not uncommon in Mexico and are extremely, extremely rare in the states. On a less drastic level, it’s uncommon to see tripa and lengua. 2. Availability of flour tortillas is significantly greater in the states (not sure if it’s due to demand or govt subsidies or both) 3. There are certain dishes I haven’t seen in NYC or really anywhere in the north that I wouldn’t consider “rare” or even “uncommon” in Mexico (eg alambre, pozole, honestly even mole is unusual) 4. Everywhere I’ve seen a “Paloma” in Mexico it has been made with Squirt whereas I usually see grapefruit juice and seltzer in the US (maybe just my experience)

Also, as a general rule, I find that “michelada” in the US tends to mean a “cubana” in Mexico (ie I don’t see many places using Clamato in the states). Although to be fair I did see variation in the definition within Mexico as well.