I’d recommend you to read about docker, specially about port mapping.
The 8080 port set in the .yml file mustn’t be changed. It’s where ownCloud will be listening inside the container.
The HTTP_PORT variable is the external port of the container, which will be mapped to the 8080 port in the container. That can be configured to the port you want (in your cause 9090, but can be changed)
What you’re doing is that the port 9090 in your host will be redirected to the 9091 in the container, but there is nothing listening in the 9091 port of the container. That’s why you cannot connect to ownCloud from the outside.
What I assume you want is that the port 80 of your host is mapped to the 8080 of the container (which is where ownCloud is running). This way you could access to ownCloud via http://my.host
Note that for HTTPS access, you’re expected to use a proxy or something similar to handle the HTTPS connection (nginx seems popular for this, I think). Basically, the flow would be client --(https)--> nginx --(http)--> ownCloud
Only nginx exposes the https port, and the connection between nginx and ownCloud happens inside the docker network (which isn’t exposed)
The Apache configuration files are nowhere to be found on my system (Ubuntu 20). Maybe the www server runs within Docker. Any help in replacing that
8080?
Yes, the apache server is inside the ownCloud’s container, and no, you aren’t expected to touch those files.