Archive a project
Go to: the project's row → the switch.
Turn it off. The project disappears from the time-logging picker, but all its history stays in reports. Turn it back on any time; the Inactive filter shows switched-off projects.
Example: the Patel year-end is lodged, so Grace switches the project off. Aisha can't log to it any more, and its 42 hours still appear in last quarter's report.