Despite modern custom, you don't really need an origin story to introduce a new character. Dr. No wasn't an origin story. The Incredibles wasn't an origin story. X-Men wasn't an origin story except for Rogue. Even debut movies that explain characters' origins don't have to be centrally about those origins, but can just briefly establish them in the introductory story about something else, like Batman '89 or Teenage Mutant Ninja Turtles (1990) or the MCU's The Incredible Hulk.
A first movie does need to introduce the character/s and premise, but we've largely forgotten that an origin story is just one possible way of doing that. Often you just need to tell the story through the eyes of a character meeting and learning about the established protagonist(s) for the first time, like TMNT or the original Hellboy movie. (For that matter, doesn't Batman '89 reveal Bruce's backstory largely through Vicki Vale's investigation?) This is a favorite method for X-Men adaptations, with the viewpoint character being Kitty Pryde in the first animated pilot, Jubilee in the '90s series, Rogue and Wolverine in the movies, Nightcrawler in Evolution, etc. For that matter, I think Marvel Girl somewhat filled that role in the X-Men's comics debut, which might be what established the pattern.
Now, there are some characters where the origin is an essential, iconic part of the story so that it makes sense to start with it. I'd say Superman and Spider-Man are the main examples of that. And that's because both their origin stories are fully realized stories, entire narrative journeys in their own right with conflict and character growth built in. Wonder Woman's origin is a whole story too, in much the same way. So you can get worthwhile movies or pilots out of retelling those fully fleshed-out origin myths.
But a lot of other origins are just a single event: Bruce Wayne's parents are gunned down and he stays mad about it. Barry Allen is struck by lightning. Abin Sur gives Hal Jordan a ring. Even something like Billy Batson getting on a train and being spirited away to meet a wizard in a cave is more a vignette than a complete narrative. If you want to build a whole movie around these origins, you need to invent most of it anyway -- but dwelling too long on such a simple origin tends to make for a shallow story, or one that rehashes the same familiar beats as previous origin stories. In cases like those, it's arguably better just to deal with the origin briefly in flashback or exposition within a story that's about the established, mature hero.
