You can archive a project to remove it from the list of projects in the left sidebar menu, while keeping a backup.
Click on the "Settings" icon in the top right corner of the window (below the user drop-down menu).
You will access the project's settings. Go down until you reach the "Archive Project" button. Click on it and then on "Confirm" to finalize the operation.
Note 1: The project will no longer be visible in your left sidebar menu. This will apply to all members assigned to this project. They will receive a notification to inform them of this archiving.
Note 2: You can archive as many projects as you want.
Access archived projects / Unarchive
"User drop-down menu"> "Archived projects": You will access the list of your archived projects and you can "Unarchive" a project to make it accessible again in your left sidebar menu.