Strange issues since update

I should have a “featured” blog post right below the menu. But the list says there are no entries (in Italian). The article is there, marked in the “featured” category, but no display. And if I go to the WP Show Posts list I cannot see the category “Featured” as an option, but in the WordPress posts list I have the one with “Featured” category.

At the same time, another list working fine on the HomePage is not showing all the articles when I click on the tag which leads to the same articles within the Blog webpage. (And I guess this is happening since version 5.5, before 5.5.1.)

https://s3nzanom3.com/blog/ (if you click on “Flow” you should see the same articles listed in the homepage, in the blog section).

Any idea? Rebuild indexes of the database? (That makes me fear disasters…)

The page I need help with: [log in to see the link]