Installed nginx proxy port app, connected the vpsXXX.opalstack.com domain name to it ...
ssh in and look around: apps/nginx_proxy (name for the app) directory
So --> no files, no config, and the web URL gives a "Good news"
Now, I'm going to guess that there is some documented, clearly explained page to explain how to use the Opal stack application to achieve what I need to accomplish.
Where is that?