After a project is complete, you can archive it to remove it from your active project list so you can preserve the work that was done.
To archive a project, go to the project page and click on the 3 dot menu [. . .] to the right of the project you want to archive.
A window will pop up asking if you want to proceed, click the button "Yes, Proceed."
The project will be removed from your active project list and appear in the "Archived" tab, next to the "Active" tab on the project page.