ssh_config is wrong
The configuration for SSH contains wrong data (It is not the public key which needs to specified there). Furthermore, I suggest to add further lines and less templates. What about this:
Host taurus
HostName taurus.hrsk.tu-dresden.de
#Put your ZIH-Login after keyword "User":
User marie
#Path to private key:
IdentityFile ~/.ssh/id_ed25519
#Don't try other keys if you have more:
IdentitiesOnly yes
#Enable X11 forwarding for graphical applications. You don't need parameter -X when invoking ssh then.
ForwardX11 yes