This show is in addition to the slew of new projects recently announced by Lucasfilm. The announcement was made in a surprise, post-credits sequence to the Season 2 finale of The Mandalorian, which sees Boba and associate Fennec Shand (Ming-Na Wen) join forces to take over a familiar crime operation from the Star Wars movies. It is assumed the series will focus on Fett's new role as a crime lord.
It has so far not been confirmed if Ming-Na Wen will be a regular in the series as Fennec Shand, although the finale implies as match. It's also so far unconfirmed if the series will follow, precede or run alongside the third season of The Mandalorian.
The Mandalorian's other direct spin-off shows, Rangers of the New Republic and Ahsoka, are not expected to debut until 2022 at the earliest. Disney are already filming Rogue One prequel mini-series Andor and in pre-production on event series Obi-Wan Kenobi, and are also developing a Lando Calrissian-focused series and The Acolyte, an original series set 200 years before The Phantom Menace. Disney are also developing animated series Visions and A Droid Story, and deep in production on The Bad Batch, a Clone Wars sequel series expected to air in 2021.