If you can't connect to the content server using 127.0.0.1:<port number> as reported by the content server, your issue goes beyond calibre.
Does the content server report the same address as the one you tried?
One experiment is to go into the firewall configuration (Windows Defender Firewall with Advanced Security) and in the properties for whatever profile is reported as active, under Inbound connections, click on enable.
If you are not on a Domain (not many people use that at home) or Private network, then you will want to set your network to private. This link may be helpful:
Make a Wi-Fi network public or private in Windows