One more data point. In my experience in Spain people definitely use estadounidense outside of legal documents. You could hear, or read, "la artista estadounide

One more data point. In my experience in Spain people definitely use estadounidense outside of legal documents. You could hear, or read, "la artista estadounidense", for instance. "Americano" is used too, as well as "afroamericano" (not "afroestadounidense").