Project geometry is backed up periodically. If a project ever becomes corrupted, you can load a backup to start afresh.
Navigate to main menu (top left) -> Advanced -> Backups
Select the project you want to load from the dropdown.
That project's backups are then listed.
Click Load on the version you'd like to view.
The geometry that was backup up at that save point loads into a new scratchpad.
To save it, create a project boundary, then save.
Only geometry is retained in the project backup. You may import layers and analytics into the new project if you need those as well.