Try refreshing the metadata for the movie.
If that does not help, Plex Dance the movie (the entire movie folder, not just the movie file).
I tested on my servers, using the file names below, Plex correctly matches the movie and shows only one trailer. If I enable Find extras for the library, Plex also displays the online trailers.
I also tested with movies with ö and ü in the name. They also worked correctly.
PMS 1.42.2.10156 and 1.43.0.10389, both on Ubuntu Linux.
Edit: Also OK on my DS918+/DSM 7.2.2/PMS 1.43.0.10389.
/movies
/Pauvres Créatures (2023)
/Pauvres Créatures (2023).mkv
/Pauvres Créatures (2023)-trailer.mkv