Technology Marches On: A fair amount of Fairy technology and equipment considered superior to the human variety at the start of the series by either the characters or the author have become decidedly less so as the years have gone by. Notable examples include wrist GPS, wafer-thin laptop computers and the iris-cam. Several Future Soldier Programs currently in development will almost certainly make the original LEP Recon jumpsuit the next casualty.
Deleted Role: Miranda Raison and Laurence Kinlan were cast as Angeline Fowl and Beechwood Short, respectively, but their scenes were cut from the final film.
Deleted Scene: The Disney+ release includes fifteen minutes of them, some of which included important plot points which instead had to be rather clumsily covered by narration from Mulch.
Early Draft Tie-In: Prior to the film's release, several tie-in books came out that depict a version of the film that is based more closely on the original novel. For example, Artemis Fowl: A Fowl Adventure depicts Artemis Fowl, Domovoi Butler and Juliet Butler standing together with a prize of fairy gold, as well as Holly Short doing the ritual and Fowl Manor being attacked by a bio-bomb. While all of these were key events in the original novel, none of them appear in the final film, though some do surface in the deleted scenes.
Lying Creator: It was confirmed in July 2018 that it will in fact solely be based on the first book. When the film came out, it did end up containing elements from the second book, including Opal Koboi as the primary villain, Artemis's chat with the psychologist Dr. Po, and the film being about Artemis Fowl rescuing his father, as opposed to his mother, who in the film is dead.
The floating fairy in white does not appear in the final film, though she is seen in a deleted scene which was made available at the same time the film was released on Disney+.
Commander Root's monologue heard at the start of the first trailer is largely excised from the final film (the only part that appears is not actually directed at Artemis), and some of the shots of Haven City seen in said trailer also do not appear.
A scene showing Holly performing the fairy ritual of burying an acorn also appeared in various trailers, but went unused in the final cut. Furthermore, the release version made no mention of the ritual, nor did it explain the significance of the acorn in fairy culture (thus rendering the acorn design of the Aculos unexplained).
No Export for You: The release date in Germany, Austria and Switzerland was pushed back to August 14, allegedly due to Covid-19-related dubbing issues. Releasing an English-only version was apparently not an option.
When Commander Root meets with Artemis to discuss terms of releasing Holly, Artemis states that while he is alive, no fairies are allowed in his property. Commander Root follows up with a knowing "while you're alive." This is a reference to the book plot where Artemis tricks the fairies into attempting to kill him in order to enter the estate, but since this subplot isn't included and Root doesn't plan to outright murder a child, this exchange is left far less meaningful and the emphasis placed on the words spoken don't actually have any further meaning.
Also in that scene, Artemis asks that they give him the Aculos "in one of those pots from under a rainbow, I presume." It's obviously a joke on the legend of leprechauns leaving gold in pots under a rainbow... which made much more sense in the original novel, when he was asking for gold.
Ferdia Shaw and Lara McDonnells screentests included dialogue explaining Roots plans and the danger of the blue rinse, suggesting this subplot was intended for inclusion at some point during development.
Release Date Change: Previously set for release on August 9, 2019 in the US, in May 2019, the film had been bumped to a May 29, 2020 release date. Then, the reshuffle in the wake of the coronavirus pandemic pulled it from that date and will release it on Disney+ on June 12, 2020.
Saved from Development Hell: Plans for the film were announced as early as 2001, but nothing came of them until 2013 when the film rights passed to Disney. The film release was announced in 2017 to be scheduled for August 2019. Despite this, release still became an issue, as it was moved to and pulled from a theatrical May 2020 release date to a digital release June 12, 2020. In all, the film went through at least four different announced writer or writer-pairs before the pair of writers actually credited in the film was settled on.