Yes. 'Heartburn' is indeed based on a true story. Nora Ephron had gone through a difficult time in her marriage which she then translated into this story. The emotions, the situations, they were all things that she had faced or witnessed first - hand, making the story feel very real and relatable to many who have also faced relationship troubles.
Since I'm not familiar with the Kareem and Nora Johnson true story, it could be about their family's struggle and success. For example, they might have come from a difficult background, but through hard work and perseverance, they achieved great things like starting a successful business or making a significant contribution to the field of art or education.
Well, without more context, it's difficult to say precisely what the Nora Jennings true story entails. It could be a story of her struggle and triumph over hardships, like she might have overcome poverty, illness or discrimination. Or perhaps it was a story of her contribution to a field such as art, science or social work.