What Really Happened 15 Years ago on the Flash(2023)

What really happened 15 years ago in the flash 2023 version. I know thawne Dosnt get stuck in 2016(s3)and he goes and messes with the legends but I wanted to make sense of og thawne disappearing because how else would Barry get his powers in the past, so maybe another version of reverse flash went back to finish the job of killing young Barry and got stuck or better yet Thawne created a time remnant of himself to maintain the timeline. Updated version Original video made by batrebel