You can archive a project if you have a Team plan, Organization plan, or Enterprise plan subscription.
☝️ Those on the deprecated Starter or Growing Business plans can also archive projects.
Anyone with an Editor role or higher can do this from the “Projects” tab of your workspace. Hover over a project and select “Archive Project” under the settings menu:
Archived projects are stored in the cloud, but they're not accessible to you or your teammates. You can reactivate them at anytime, as long as you have a subscription with enough project slots.