Most of the US, in cities, you can find solid Mexican food. Chicago probably has the best "authentic" non-Cali Mexican in the country even. You won't have to worry just might have to hunt a bit.

The rest of the world? Yea you're screwed. I found one place in Berlin that did legit Mexican because it was run by Mexicans (Santa Maria in Kruezeberg) but that's literally the only decent Mexican I've found in the 50+ countries I've visited and trust me, I've looked in all of them.

Good news is you can find the ingredients for good Mexican in pretty much all of them and do it yourself. The hardest to source is proper jalapeños or any dried peppers, but there's usually a speciality shop somewhere that will be able to give you most of what you need. Cilantro can also be a bit of a pain, but it's way easier than it used to be even 10 years ago.

The worry is real. You cannot find a decent mission burrito afield. It really a local specialty of San Francisco. I suspect the same is true for burritos found in San Diego. And those tacos in Texas, on flour tortillas, well those aren’t tacos at all but incomplete and unfinished burritos. OK if you want to rebrand a half assed burrito and call it a taco go right ahead. And none of it is a sandwich - not burgers, dogs, falafel, shawarma, gyros, burritos or tacos. A taco is not a sandwich