How to show a category in the homepage grid?

Hi, this, https://www.emilianoperani.com/travel/sud-america/, is a page, not a post category. If you wish that to show as your main page instead of your posts, then go to Customize > Homepage Settings and set that page as your static home page. You would also then want to create a page for your posts and publish it (no content in that page) and at Customize > Homepage Settings set that page as your posts page.

If you are wanting only the posts from a sud-america category (you have no published posts in that category right now) showing on the main page, that can be done with the following custom CSS.

.blog .site-content .hentry {
  display: none;
}
.blog .site-content .hentry.category-sud-america {
  display: block;
}

Thank you for the reply.
I solved it simply creating a fake post in the homepage and redirecting it to the page above (I installed the Quick Page/Post Redirect plugin to do that)

You are welcome, and glad you found a solution.