As a black man in a white-dominated society, Othello is constantly aware of the racism and prejudice that he faces. This makes him feel insecure and vulnerable, and it makes him more susceptible to jealousy. When Iago plants seeds of doubt in Othello's mind about Desdemona's fidelity, Othello is quick to believe him. He is so consumed by jealousy that he is willing to kill the woman he loves and then kill himself.
In contrast to this, it would be much harder for a white Othello to feel the same level of jealousy and insecurity. As a white man, he would be more likely to feel confident and secure in his position in society. He would also be less likely to feel threatened by other men. As a result, he would be less likely to believe Iago's lies about Desdemona.
Of course, there are many other factors that would contribute to how the novel of Othello would be different if he were white. However, the role of race is undeniable. This theme is one of the most important aspects of the novel, and it would be fundamentally altered if Othello were not a black man.
Despite the differences, if the protagonist were white, the story would still be an important and powerful one. It would explore the same themes of love, jealousy, and betrayal, but it would do so in a different way. If the protagonist were white, it might be more relatable to the majority of people.