Hi,
That looks like the simple post categories taxonomy. Enabling this option will return the post categories as results: https://i.imgur.com/Lxfpycj.png
On the other hand, which is strange, when I type a category in the search form, the search suggestions work, but when I hit “enter”, it’s impossible, I can only select suggestions.
If you mean when redirected to the results page, then make sure that the results override feature is enabled. That should do the trick.