Potterheads were shocked to learn that Warwick Davis, who played Filius Flitwick in all eight Harry Potter movies, would play the role again in the HBO series. It is important to remember that Davis is not reprising his role from the Potter movies, just playing a different version of the same character. The HBO series takes place in a new continuity as it follows new actors playing Harry, Ron, and Hermione.
While Davis played the Charms Professor Flitwick in all eight Potter movies, his character underwent a huge transformation in the third movie, Harry Potter and the Prisoner of Azkaban. While he looks whimsical and old in the adaptation of the first two books, his appearance changed drastically since Prisoner of Azkaban, as he looks considerably younger and less whimsical.
Moreover, Prisoner of Azkaban and Order of the Phoenix even showed him teaching a class that isn't Charms. That's why the HBO series should establish two things from the very beginning about the Charms professor: his look, and his position as the professor of Charms and the Head of Ravenclaw House.
Explaining Professor Flitwick's transformation in the Harry Potter movies:

The first two movies directed by Chris Columbus featured a Flitwick who looked very different from what he looked like in the rest of the movie franchise. It was Alfonso Cuarón who changed the look of Hogwarts and characters like Flitwick and Draco Malfoy. Cuarón's changes stuck around, be it the look of Hogwarts or the characters, including those of Draco and Flitwick.
But the third movie made another change to Filius Flitwick's character. The only time we see Filius Flitwick teach the charms class in the entire film franchise is in the first one, Philosopher's Stone. He is mostly in the background in the second movie. In Prisoner of Azkaban, we see him conducting a choir, and he stuck around as the choir master in the entire franchise.
This change has been divisive amongst fans, as some believe that this change does not matter, as Flitwick is a background character, while others point out that the Head of Ravenclaw was a powerful wizard who went toe-to-toe with Voldemort and survived him in the books. Canonically, he is one of the most powerful wizards in the Wizarding World.
The HBO series can present a more respectful Filius Flitwick:
The HBO Harry Potter show has a chance to vastly improve upon the movies, as they used the character for comedic relief and nothing more. The writers working on the series have a chance to plant the seeds for Flitwick's expertise as a duelling champion right from the first season, which adapts the first book, Philosopher's Stone.
Warwick Davis's return only makes things special, as the actor gets another chance to impress the audience with the new version of the character he played between 2001 and 2011. Setting his look and position as the Head of Ravenclaw will indicate to the viewers that they should not underestimate him based on his height.
The HBO Harry Potter show is releasing sometime in 2027. What do you think about Warwick Davis's return to the Wizarding World?