I don't think there would be a lot of fanfiction like that. Hinata has always been loyal to Naruto. In the Naruto universe, their relationship is based on a lot of development and mutual understanding. So it's hard to imagine a scenario where Hinata would cheat on Naruto with Boruto in a legitimate fanfiction.
Another reason could be in a fan - created scenario where there are secrets involved. Hinata might be keeping a secret from Naruto that, when revealed, makes Naruto feel betrayed or deceived. This sense of betrayal could easily turn into anger. For instance, if Hinata has a connection to an enemy that she's been hiding from Naruto.
One possible plot could be that Boruto and Hinata have a deep emotional bond that develops over time. They face many challenges in the Hidden Leaf Village together, which brings them closer. As a result of their love and closeness, Hinata becomes pregnant, and then they have to deal with the reactions of their family and friends, like Naruto's reaction as Boruto's father and also how the village will perceive this new development.
One reason could be Boruto's recklessness. In fanfiction, Boruto might engage in dangerous stunts or actions that go against Naruto's teachings. For example, if Boruto were to use a forbidden jutsu without fully understanding the consequences, Naruto would be angry as it not only endangers Boruto but also those around him.
One idea could be to focus on their anticipation and preparation for the baby. They might discuss names, decorate the nursery, and Hinata could be shown getting advice from her family. Naruto, on the other hand, would be excited but also a bit nervous about becoming a father.
Danzo could also be the one to make Naruto angry. Danzo's underhanded tactics and secrets might be exposed in the fanfiction, and if they were to directly harm Naruto's friends or the village, Naruto would be furious at his actions.
To start a fanfic about Naruto and Hinata making Boruto, first think about the setting. You could begin with a simple family scene at home in Konoha. Maybe Naruto is just back from a mission and Hinata is preparing dinner while Boruto is showing Naruto his new ninja moves. Then, start writing down their dialogues. For example, Naruto could be saying how proud he is of Boruto's progress. Keep it simple and build on their relationships as a family.
Well, there's this fanfiction titled 'Hinata's Influence on Boruto'. It delves deep into how Hinata's gentle nature and strong values shape Boruto's character as he grows. It has some really heart - warming scenes between mother and son. And then there's 'Boruto's Path to Greatness' which also involves Naruto and Hinata in the background, guiding Boruto on his ninja journey.
One idea could be a story where Boruto and Himawari discover an old diary of Naruto's from his early days as a ninja. Hinata helps them understand the context and the values their father held. They then use those lessons to face a new threat in the village.
One possible reason could be misrepresentation of her character. In some fanfictions, authors might change her personality to fit a certain plot, like making her overly jealous or mean, which would be out of character for the gentle Hinata. This could make her seem unlikable and thus anger fans who love the original Hinata.