Premieres sometime in 2024. English article for more info and character visuals. Synopsis from AniList:
Why does no one remembers the true world...!"
The era when the great race of the five tribes competing for hegemony on the ground ended with the victory of mankind led by hero Sid. However, that world was suddenly "overwritten" in front of a boy Kai. In the rewritten world, Kai saw the scene where humans lost to the five tribal wars because of the absence of hero Sid—here dragons and demons dominate the ground, and Kai is a forgotten existence from all human beings. However, after encountering the mysterious girl Rinne, Kai decides to break this rewritten destiny. In a world without heroes, he inherits the hero's sword and martial art and challenges the mighty enemy races who reign.
I have seen this title translated a couple different ways in different articles. Even on the teaser visual I linked to here, it is translated as "Why nobody remembers my world?". However, out of the couple variations I saw, I decided to go with the one Crunchyroll used as it sounds the most natural to my native English ears.
I am far from fluent in Japanese, but the native title is 「なぜ僕の世界を誰も覚えていないのか？」 (Naze Boku no Sekai wo Daremo Oboeteinai no ka?, literally: why my world everybody doesn't remember?). My reading of this is that the title on the poster is a pretty literal translation of the native title even if it sounds awkward.
Anyway, that is just some quick translators' notes for why the visual might not match up with the title I used in the post.
The french manga, that got release choose the translation: Why Nobody Remembers My World. I have the feeling we will see a lot different for this title