This is too good to leave in a comment
Let it be admitted at the outset that the determination of art as expression has its correctness. The notion that art is expression is just as indisputable as the statement that the motorcycle is something that makes noise. Every mechanic would laugh at such a determination of the essence of the machine. But no one laughs when it has been said for a long time that art is expression. Certainly, the Acropolis is an expression of the Greeks, and the Naumburg Cathedral is an expression of the Germans, and the 'baa' is an expression of the sheep. Indeed, the artwork is simply a special expression, i.e., its own "baa" — probably. The work, however, is not a work because it is an expression. Rather, it is an expression because it is a work. The characterization of the work as expression not only contributes nothing to the determination of the work-being, but instead already forestalls any actual inquiry into this Beyng.
Ironically, Heidegger appears to have appreciated works by Expressionist artists (Kandinsky, Klee) while loathing the Cubists