This is maybe more of an Agile or Scrum question, but here goes. As a technical writer, some of my documentation work for a project aligns with specific features for the project, and some of it pertains to the project overall. It has been challenging to track my docs to-dos in terms of Epics, Stories, sub-tasks, etc. (I usually use Jira, this current project is tracking in Azure DevOps but the principles are the same.)
I typically don't operate at the Portfolio Epic or Initiative level, those items are determined by management.
Some docs work for the entire project could potentially be at the Epic level, since some of it will take multiple sprints for it to be completed, or it pertains to the entire documentation site. (These would be tasks like information architecture, setting up feedback mechanisms or analytics, branding, search config, about this site, etc.)
Some docs work aligns with a specific feature. This could be docs on how to setup a widget, which get developed while the widget setup module is being built. "How to use the deploy module" docs work would align with the development work on the deploy module itself, so that when the module is ready the docs are ready too.
I'm pretty sure I need my very own Epic to capture the work that doesn't pertain to a feature. How do the rest of you do it?