Shadow should absolutely get a spinoff after stealing the show in Sonic the Hedgehog 3, but it would need to be different from the series’ other spinoff. After teasing the character in the post-credits scene of Sonic 2, Keanu Reeves officially debuted his version of Shadow in Sonic the Hedgehog 3. The story of Sonic 3 begins with Shadow escaping from Prison Island in Tokyo Bay, Japan, and wreaking havoc on the city. Sonic, Tails, and Knuckles are recruited by the Guardian Unit of Nations to take on Shadow, but quickly realize the Black Blur is far too powerful.

https://screenrant.com/shadow-spinoff-movie-not-tv-show-knuckles-lesson-op-ed/