Editors & Commenters can leave a project (while maintaining access to it) in order to clean up their workspace.

Project-specific editors & project-specific Commenters may leave projects at will, but will need to request access from a Billing Manager or be invited by an editor, to join those projects again.

From the Projects page, click the kebab menu on the project you'd like to leave, and choose Access permissions.

Click the kebab menu to the right of your name to remove yourself from the list of users with access. (You may have to scroll to see your name if there are several other users in the project.)

If it is a project you can re-join, it will now be listed below the projects you have access to. (If you had project-specific access to it, it will not be listed here and you'll need to re-request access)