Rugrats (2021)

On their official Instagram account, Nickelodeon had announced that they were going to be making a new Rugrats movie set for a release date of November 13, 2020. It was confirmed that the film would be a live action and CGI animated hybrid unlike the previous three films. However, due to unknown reasons, the film was pushed back to January 29, 2021 before finally being pulled from Paramount's release schedule on November 12, 2019.

Plot:
Unknown

Why it was cancelled:
It is speculated that due to the overwhelming praise of the Sonic the Hedgehog 2020 trailer, Paramount decided to remove two upcoming live action CGI hybrid movies from their release schedule. One of those movies was the upcoming Rugrats movie.

Results:
Paramount removed the movie from their release schedule as of November 12, 2019. It is currently unknown at the moment if the film will ever be released.

Reference:
https://youtu.be/tUqdM15O62k