If you only have one IP address, you need to set all sites that are using HTTPS to require Server Name Identification so that IIS knows what cert to use for clients connecting to which site. Either each site needs to use SNI, or you must use different ports, or different IP addresses.
By default most webservers assume that if you're coming to them with HTTPS,...
Yes, this is possible.
Make your own software listen on local loopback alone, e.g. on localhost:8080.
Terminate TLS with NGINX.
listen 443 ssl;
As a ...
In general there is absolutely no security benefit to encrypting traffic between services running on the same host.
(Localhost traffic can only be intercepted by an attacker that has full access to the server. When they can do that they can already access all data stored on your server directly (from the file system) and won't need to bother with ...