Installation successfull / Problem with root

Hi guys

I have some problem with the root directories here and not sure if it is a server based problem or wordpress based one.
My blog is on https://www.edelrot.net/blog/index.php
Click around and you ll get the 404 error message saying “/whatever.php could not be found on this server”.

But if I give in the address manually i can reach the pages.

Any help appreciated!