This is both true and false because Americans as a category contains both the "middle" class (professional/managerial, petty bourgeois/landlord, cop, etc) as well as the lower working class: wage workers and imprisoned labor.

The former has been the ideological and symbolic essence of Americanism, the focal point of US culture and commodity production, despite being a smaller subclass than the lower workers. They've gotten the lion's share of any imperial spoils that weren't taken by the large bourgeoisie. Highways and suburbs and theme parks and restaurants exist for these people. They're the image many people think of when they hear the word "American", an image that obscures the domestic wage work that props them up as well as the international expropriation of resources.

This illusion even has its effect on the wage workers. Deprived of real proletarian culture and language, they absorb the manufactured culture of the "middle class", which functions as a false consciousness. Cheap commodities and consumer debt help bolster this consciousness while also heightening their exploitation.

The "middle" subclass (whatever you want to call it) has been getting eaten away for the last few decades. More and more people have shifted from the "real" middle consumer class to the image of middle consumption that's propped up by debt and cheaper (and increasingly shittier) commodities. Many aren't consciously aware of the change, most don't understand the mechanisms that caused it.

But we still exist in the ruins of this mythical middle class, where resources are wasted building too-big houses, fast food joints, oversized cars and roads. Utilitarian commodities often aren't produced at scale so wage workers are stuck trying to live with inefficient scraps of the petty bourgeoisie. There aren't enough small cars (and few buses/trains because that's counter to the petty bourgeois image), there aren't enough apartments, there aren't enough healthy food distribution centers.

There often just aren't cheap options. And even when there are, people are subject to increasingly-complex psychological and social manipulation to overconsume.

If you haven't been thrust into the reserve army of labor or whatever shade of lumpen, and you can avoid the psychological manipulation to overconsume, and you don't have kids, you might be able to live a fairly comfortable, if tenuous, life. That opportunity certainly isn't equally accessible everywhere in the world, so it's a sort of privilege.

But it's not a stable class. The American form of commodity production is crumbling. There's nothing to take its place, domestically. Just petty bourgeois ruins.