systemd-networkd.socket failed. Any ideas on what to do?

I have a problem with the Internet connection on my Server. I cannot use Filezilla or Webmin because my systemd-networkd.socket seems to be buggy or something. Can you help me? This is my output:

$ systemctl

systemd-networkd.socket loaded failed failed

$ systemctl status systemd-networkd.socket

Loaded: loaded (/lib/systemd/system/systemd-networkd.socket; enabled; vendor preset: enabled)

Active: failed (Result: service-start-limt-hit)

Also, I get the message:

Jan 20 16:34:21 exampleserver systemd[1]:systemd-networkd.socket: Socket service systemd-networkd.service already active, refusing.

Failed to listen on Network Service Netlink Socket

On ubuntu 20.04, you can open the application systemd-manager. Then click on the Services button in top bar, a drop-down will open. You will need to select the option 'Sockets'. Left panel will show list of socket services, there you can find the service name as 'systemd-networkd'. Against that service, there must be two green tick marks. If not, then select that service and click on 'enable' button in top bar and then click on 'Start' button (green button) to start the service. This will make the two green ticks against that service in left panel.