To get non-active projects out of the way I simply add the letter z to the start of the name. This makes them drop to the bottom of the list of projects. Doesn’t prevent the notes turning up in searches etc, but it helps reduce clutter.
(Looking forward to real archiving in due course!)
What I did: A new Category “zzz ARCHIVE” with sub-folders in which I move finished projects.
This keeps the left sidebar shorter (and less clutter).
I also hope to see a true Archive in which I move finished projects.
I have two categories for that, one is ** Archived Projects **, the other one is * Dropped Projects *. I put them at the top using asterisks *, hiding them clicking on the title. But I agree that it would be great to have a proper system to archive the completed projects.
Not a native solution, but I view Agenda as something for current projects. Once a project needs to be archived, I export it as a PDF and save it to DEVONThink.