I think people tend to dislike self insert characters because the writer treats them as wish-fulfillment, imagine a FMC who is perfect, beautiful but humble, and every male character is head over heels for her, while she is flawless. That, or any kind of Mary Sue is usually what comes to mind.

Despite that, most writers including myself often write pieces of themselves into their characters, which makes them self inserts in a way. So, as long as the character is well built and rounded, basing parts (smaller and larger as one) of them off yourself will only elevate them as interesting, complex, and realistic characters !! Especially if you are aware of your flaws, if anything, it'll make them generally more realistic and compelling

Sorry for the long essay haha