About 12% has been lost to international competition, which isn’t nothing.
But with global markets and supply chains, companies have factories around the world in addition to factories in the United States, not instead of (though it varies by industry).
In many big manufacturing sectors, American output is up and American employment is way down.
For example, in the last 20 years, US production of steel and other metals has increased 38%, while shedding 265,000 jobs. Robots make the mills much more efficient.
There’s a citation in the article (here if you missed it).