When does Harvey Birdman, Attorney at Law return?

Harvey Birdman, Attorney at Law is an adult animated television sitcom. The series was created by Michael Ouweleen and Erik Richter for Cartoon Network's late-night programming block, Adult Swim. The pilot first aired as a sneak peek on Cartoon Network on December 30, 2000. It ended on September 2, 2001, with a total of 39 episodes, over the course of four seasons. A spin-off, Birdgirl, premiered on April 4, 2021.
Harvey Birdman, Attorney at Law is the first Williams Street cartoon to maintain continuity through the entire series. The series uses a surrealist style of comedy, featuring characters, objects, and jokes that are briefly introduced and rarely referenced thereafter. Harvey's clients are primarily characters taken from the Hanna-Barbera cartoon series of the same era.