It is a reference to the General Agreement on Tariffs and Trade. Gen alpha is very interested in the history of international trade and the rise of the global market economy.
I work with kids, it essentially means ass but has a sexualized context to it. Most kids approaching high school realize this and don't use it as frequently around me, but younger kids seem to think it just means butt. Again this is just my experience and it could vary from place to place
Yes, my kids and their friends (10-13 yo) say it all the time and it's pretty uncomfortable. They also say hawk tuah to just mean spit which is much more uncomfortable.