Biographical information can be found here, here, and in German here.
Birkle's non-religious art can be categorized as Expressionist, or Neue Sachlichkeit, but not usually extremely so in either case. Given that I am not fond of either genre, it follows that Birkle's paintings do not appeal to me. But perhaps you might like them, or find them interesting.
A self-portrait perhaps from the 1920s.
Self-portrait when he was a war artist stationed in France. The uniform is military style, but the epaulet indicates a non-combat status.
Self-portrait wearing a leather jacket. Birkle appears to be in his 50s here.
An example of landscape painting.
Ku-damm was and is Berlin's main shopping street. This was painted during the post- Great War hyperinflation of German currency, a time of economic chaos and hardship.
Early Spring in a Bavaraian Wood.
An art dealer.
A Berlin scene in the spirit of Ernst Kirchner's prewar Berlin street setting paintings.
Birkle's women all seem to have very long fingers.
Painted while a war artist. That's a German flag related to ocean service on the boat.