UPDATE: I figured it out; I managed to adjust the Date-settings. I didn’t change the grafana.ini (as I couldn’t because the data-entries are not there) but changed the default.ini instead:
PATH: /usr/share/grafana/conf
Request: If I did it wrong and should have adjusted the grafana.ini instead of the default.ini please let me know.
Now I changed it to European setting with day-month-year format (instead of year-month-day) in the default.ini file and restarted the server. Now it is fine.
Admin screen