Starting from version 3.25 PC client uses Windows IPP component for communication between Windows spooler and PC client core service.

The requirements are following:

• Internet Printing Client feature should be installed (this should be done by the installer, if not enabled on the OS instance)
• The Turn off printing over HTTP (or DisableHttpPrinting) policy must be set to OFF ('0')

To quickly check if the policy is disabled, verify the registry setting and make sure it's set to '0'

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\Printers\]
DisableHTTPPrinting = 0

The communication between Windows Spooler and HCP Client is over IPP (HTTP). The communication is only on localhost. 

The communication between HCP Client and Server is still protected by TLS.