Hi,
Thank you for the details, it helps a lot!
I have logged-in, checked the configuration, but that is definitely okay. Then I checked the theme editor, and the issue is the search.php file in the theme directory – it does not output the results whatsoever. It loops through, but nothing is ever printed: https://i.imgur.com/KZwNpxN.png
There are matches, and they get to the results handler, but they are not printed by the theme.