No, The Idol’s lead character Jocelyn isn’t based on Britney Spears, as confirmed by the character’s actor and co-creator Sam Levinson – however, there are numerous reasons why people assumed this was the case.
here is a link to the article that breaks it down more for those that need more details.
https://www.dexerto.com/tv-movies/is-the-idol-based-on-britney-spears-2167026/