Avoiding duplcate posts on the main page

Hi, I have several pages on my site. Each of them displays posts belonging to a certain category. For example, the “Recipes” page displays only posts from the “Recipes” category, the “Jokes” page displays only posts from the “Jokes” category, and so on. The main page displays posts from all the categories. Suddenly I noticed that there are duplicate posts on the main page. For example, the “Recipe 1” post appears there 2 times. Both of these posts have the same address. Interestingly, these posts are not repeated in the “Recipes” category, they are only repeated on the main page. Why does it happen?