Hi there @idoki,
I wondering if you are chasing your tail, I tried to check the dns enteries which your two domains control panel would be set up
gives an ip address of 18.104.22.168 which does take you to an easyname parked domain message.
you can check the system.yaml
but see it forwards to a sub directory of /lb
so you might find there is a redirect to the domain running as well as the fleegeelteren-lëtzebuerg.lu doesnt report a ip address.
Maybe just do a test and install a fresh copy of grav in to a sub directory, lets say grav-test and then see if you can get access to the webspace by using the ip and the subdirectory in the browser by
to ensure your host (easyspace) is accessible, is something weird happens, you know it either the system.yaml or a .htaccess or redirect or custom route that has been setup
Just to add, i thought I would ping the address of the working website and got this link
https://xn--fleegeelteren-ltzebuerg-2dc.lu/lb notice the prefix xn-- , so some sort of redirect in place
which traced to the visible site being on https://kasserver.com/