How to change the connection descriptor used by Oracle Enterprise Manager

May the reason be why I installed Oracle as desktop class instead of server class?

No, 'Desktop Class' just means you only get basic choices from the installer¹, according to the docs:

• Desktop Class—This installation class is most appropriate for laptop or desktop computers. It includes a starter database and requires minimal configuration.

• Server Class—This installation class is for servers, such as you would find in a data center, or used to support enterprise-level applications. Choose this installation class if you need access to advanced configuration options.

During a Desktop Class installation, you make only basic choices. For a Server Class installation, you choose either typical installation (where you make only basic choices) or advanced installation.

During a Desktop Class or a typical installation, Oracle Database automatically installs the sample schemas.

You'll need to go through the kind of troubleshooting steps suggested in the comments to find out what is causing the ORA-12545 error:

An ORA-12545 error occurs when the client is not able to contact the listener on the node specified. For example: when the listener has not been started on the node, if the node address has been specified incorrectly, or a firewall blocks access.

_{¹ So 'Desktop Class' and 'Server Class' are poor names for the installation types. 'Basic' and 'Custom' might be better?}

I do not have any clear explanation for this problem solution. However I used SID instead of service name in connection string and it worked.

Edit: A service name is more flexible than a SID would be. A database can dynamically register with a listener using one or more service names. In fact, more than one database can register with a listener using the same service name.A database on the other hand has a single SID. And a single SID goes to a single database. So I would say it is safe to use SID rather than service name.