A quick note on copyright: Fantastic Mr. Fox is owned by 20th Century Fox (now 20th Century Studios/Disney). Because the film is based on a Roald Dahl book from 1970, is widely available. The movie is not. The film will not enter the public domain until 2105 at the earliest. So, if a website claims the full 2009 movie is "free in the public domain," that is a red flag.
You can find "Fantastic Mr. Fox" on various streaming platforms and online archives. Here are a few options: fantastic mr fox full movie internet archive