Not at all. My Dress Up Darling manga is far from being cancelled. It continues to attract a large fan base and the creators are actively working on new chapters.
First, really understand the characters. Know their personalities, likes, and dislikes from the original work. Then, come up with an interesting plot. It could be a new cosplay project they take on or a relationship - building story. Also, use vivid descriptions, especially when it comes to the cosplay costumes and the process of making them.