When Warner Bros. first launched the DCEU, it was the plan to give each member of the Justice League their own movie; for some, such as Wonder Woman (Gal Gadot) and Aquaman (Jason Momoa), those plans came to fruition, but others, like poor Barry Allen (Ezra Miller), have found their respective projects languishing in development hell for years. Seth Grahame-Smith (ABRAHAM LINCOLN: VAMPIRE HUNTER) was originally on-board to write and direct the film back in 2015, but he soon exited the project and was replaced by Rick Famuyiwa (DOPE), who also wound up leaving over creative differences. The studio then picked John Francis Daley and Jonathan Goldstein (SPIDER-MAN: HOMECOMING) to helm the film, but they also departed the project and were ultimately replaced by Andy Muschietti (IT).
Throughout all this tumultuous development, the story of THE FLASH movie was said to be an adaptation of the popular Flashpoint comic story-line, but while speaking with That Hashtag Show, Muschietti reportedly said that the film will be a "different version of Flashpoint than you’re expecting." What does that mean? I haven't the foggiest, and it would probably be best to take it with a grain of salt for now.
The Flashpoint story-line in DC Comics centered around Barry Allen awakening in an altered DC universe to discover that he's the only one aware of some fairly significant differences from his regular timeline, such as a destructive war between Wonder Woman and Aquaman, Superman being held captive in an underground laboratory, and that Thomas Wayne, Bruce's father, is Batman. Exactly how Andy Muschietti's take on these events will be different remains to be seen, but given how the DCEU has evolved over the years since these initial projects were first announced, it makes sense that they may not be on the same path they once were. Previously, Muschietti has said that what captivated him about THE FLASH was the "human drama" in it. "The human feelings and emotions that play in the drama [of it]." Muschietti said. "It’s going to be fun, too. I can’t promise that there will be any horror [elements in it], really, but it’s a beautiful human story."
Warner Bros. recently slated THE FLASH for a July 1, 2022 release.