According to Atari's post, the game "was canceled in development when Atari 2600 game production ended in 1990, ending a 13-year run." This new release is limited to just 500 cartridges.

Atari Will Soon Produce Its First New 2600 Cartridge Game In Over 30 Years Mr. Run And Jump is getting an official Atari 2600 cartridge limited edition. By Grace Benfell on June 13, 2023 at 8:31AM PDT ...

The game is called Sonar, and was developed by programmer Brad Stewart during his time at Atari. According to Atari Protos, Sonar was one of two unreleased Atari 2600 games Stewart worked on ...