A number of differences are present between the manga and the anime. One of the most important arc which were present on the manga and removed on the anime was the Goldy Pond arc.
The removal of the Goldy Pond arc sweeps away a number of character from the Promised Neverland such as the Pouchers, Yugo and his friend Lucas.
Another difference stands on Norman's comeback. The return of Norman in the manga was one of the best twists of the series. However, in the anime, everything was rushed. The audience didn’t have time to miss Norman and his appearance seemed far too convenient. Norman was re-introduced alongside Emma and Ray too early on the anime without the needed precautions.
Moreover, the royal family is barely mentioned on The Promised Neverland season 2 while its presence had a core role on the conflict with Norman.