What is harbour 5986 for?

Windows Administration. The protocol or service generally associated is WinRM HTTPS.

Transport Protocol

TCP

Safety precautions

Use valid certificates and limit sources.

Should we open this port in the firewall?

Only if a service is actually needed the use it. Apply the principle of any privilege: limit the authorized sources, destinations and interfaces, and then log connections when relevant.

How do I check this port?

Test-NetConnection SERVER -Port 5986

Under Linux, you can use nc -vz SERVER 5986.

Port/service associations are common conventions. An application can be configured on another port.