Red Dead Redemption 2 is a remarkably polished game, but it does have some glitches and bugs in it. A lot of these can be hilarious, but there’s some… interesting ones, that can play pretty hard to the nostalgia players may have for the original game that came out in 2010.
One of these glitches is one that lets you get to Mexico. It’s a part of the map that’s in the game, but is basically completely empty. You can also glitch to Guarma Island, which is based on Cuba, and is similarly empty. Presumably this is just unused map data that was left in the game—but for anyone who wants to go there anyway, there is an easy way to do it, although, as I am sure you have caught on to by now, it requires you glitching your game.
You also need to have completed the game entirely to be able to use the glitch. This means you must have completed the final mission.
Keeping all of this mind, and being mindful of the fact that these videos almost certainly have spoilers, you can watch them to figure out how to glitch outside of the playable map area in the game.