Hi There, thank you. I fixed it. I had to upload a new version of Joomla 5.1 to fix this issue. I uploaded all files, except for the configuriation file of course, and that did the trick. Now I'm stuck with finding the language file for the Countdown module, for which I mad a new thread. Help is very welcome.
PS: yes, I know about the certification/warning. It's just a test site to show friend before I make her website on different server.