For your first question:
To remove "completed" epics from the Agile backlog, click on the arrow to the right of the epic name in the backlog and select "mark as done." This will remove the Epic from your Epic list on the Backlog.
Second question: Are you asking if you can hide completed stories viewing an epic?
I have multiple projects that use variations of the same base workflow. The variations depend on the requirements of the project or issue type. The variations mostly come in the form of new statuses ...
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