Couchbase-server official docker image starting but cant connect to it && no log errors about docker HOT 1 CLOSED

This GitHub repo really isn't the right place to seek support for running the product. I'd suggest trying on the Couchbase Forums: https://forums.couchbase.com/

My best immediate guess about your problem is that your OS is configured to block some ports (iptables?), or that some security system like AppArmor is interfering with Docker's ability to listen on those ports or for your browser to connect to them. Another thing you could try would be to access http://127.0.0.1:8091/ rather than http://localhost:8091/ - I have seen cases where the former worked and the latter didn't, although I cannot explain why. As an experiment, try running

docker run -d -p 8091:80 nginx

and see if connecting to either http://127.0.0.1:8091/ or http://localhost:8091/ works.

In case it's helpful, a couple additional thoughts on the information you provided:

1. A Docker container isn't running systemd or SysV init, so running the service command isn't a meaningful thing to do.
2. There's no need to have the |grep couchbase on your ps command, because inside a container, the only processes that should be running are the ones for the container itself (and, in your case, the interactive shell processes). You're filtering out a lot of processes that are part of Couchbase Server; not all of them have couchbase anywhere on the line, since "ps" is truncating the username to couchba+ as you can see.
3. On a freshly-started Couchbase Server enterprise-7.0.3 container, I see 30 processes owned by the couchbase user, plus two owned by root (runsvdir and runsv).
4. error.log would only have contents if there were any errors. The fact that it's empty is probably a good sign. Another thing you could check would be babysitter.log - somewhere in there (probably at the end) it should say "Booted. Waiting for shutdown request" if Server came fully online.

from docker.