Mainly "cross platform". Many people would interpret that as [desktop] platforms, e.g. Linux/Windows/Mac OS. Especially if you weren't previously aware of what Flutter is.
Adding a "mobile" in there somewhere would be a significant improvement.
In addition "movie app" is a bit underspecified. Maybe it's for managing movies? Editing them? Playing them?
Especially when both confusions are combined, it can be easy to get the wrong idea of what the submission is.
"inKino - A cross platform movie and showtime browser for Finnkino cinemas, made with Flutter."
"inKino - a showtime browser for Finnkino cinemas"