Building a basic factory is up to 2 years, depending on size, then you have to recruit all kinds of workers, many of which might not be readily available in a short notice of time, and might require college education. Manufacturing isn't just driving in the screws on an iPhone (which is more like glued together).
This is all assuming they'll use all US components, which are available, and at least higher-end US made capacitors are on the same level as their Japanese counterparts. The issue would be scope. Don't know what happened to that TSMC factory after Trump axing the CHIPS act. However, that "all American" Nintendo Switch 2 would cost a small fortune, and would be needed to be made much longer lasting that otherwise, since it's now incompatible with the notion of cheap and short lived products, which those on the top wouldn't approve.