Despite those brushes with Modernism, following Great War service in Italy's elite Alpini forces, Oppi briefly associated with the Novocento (Twentieth Century) movement, a more traditional-yet-Modernist-inspired group.
By the 1930s he focused on religious works. In World War 2 he rejoined the Alpini with the rank of lieutenant colonel, but his health failed perhaps from cancer and he died about age 53.
An example of Oppi's prewar work. The face strikes me as being a dialed-down version of what Kees van Dongen was doing at the time.
This "Lady at the Window" looks like his wife.
His wife posed against a Venetian background.
The young bride / wife. Note the tile flooring and one-point perspective in the background that harkens back to classical Italian paintings.
Like most artists, Oppi painted some portraits to earn income.
Another portrait of his wife. He also painted nearly identical half-view of her the same year.