I've configured my router in the following way since there is no "manual" option:

service provider: www.gnudip.cheapnet.net
hostname: solrhost.myddns.rocks
username: seigi
password: ********

and nothing else is required.

Then I have my port forwarding configured, ports opened in my firewall and the client running on my pc which seems to work properly and updates my ip every 60 seconds.
Furthermore my private ip is set as static.

The issue is that if I try a connection to my host from another network I have a "problem loading page" after a while. If I try from my pc instead, for what it could be meaningfull, it opens the configuration page of my router.

Are you able to access your host from another network using the external IP address of your router? Its possible that your router does not allow access from the general internet due to security reasons, though this could be changed in the router settings (sometimes called Remote GUI). Could you confirm that the hostname is pointing to the external IP address by verifying using the below link:

https://checkip.dynu.com