https://www.cbr.com/grant-gustin-the-flash-movie-cameo-rumors/

The Flash star Grant Gustin acknowledges rumors that he will have a cameo in Warner Bros. and DC's upcoming The Flash movie starring Ezra Miller.

Grant Gustin's Flash Movie Snub Is An Insult After 10 Years Of Playing Barry Allen (https://screenrant.com/the-flash-movie-no-grant-gustin-barry-allen-cameo-insult/)

Grant Gustin debuted as Barry Allen in 2013 on The CW and has since built a brilliant legacy as the DC hero, but 2023's The Flash will ignore him.

pretty sure bet that the Flash movie is going to be a huge bomb - nobody likes the weird new adaptation of the character that has absolutely no relation to the classic comicbook characer portrayed by an actor with a number of controversial issues and no real reason to stick with him for this role or go forward with thi movie at all.