“Corned beef is not Irish. Irish immigrants in the United States adopting it from seeing Jewish immigrants eating it.”
Irish corned beef was produced in Ireland before they came to the U.S.
Corned was simply a way of preserving meat. That made it cheaper than fresh meat. People all over the world probably did it. It isn’t some kind of specifically Nationally recognized dish in Ireland. I’ve heard Irish in Ireland actually ask WHY corned beef is associated in the American mind with the Irish.
I imagine almost every culture had salted beef.