There are two ways to save a project: [Auto-save] for when there is a change, and clicking on the [Save] button to manually save.
▪ Auto-save: Whenever there is a change, the project auto-saves itself periodically.
▪ Manual save: Click the [Save project] button on the top right to manually save the project.
▪ Check the record: Hover your mouse over the [Save project] button to check the last time the project was saved.
▪ Version history: Check the stored history at [File > Version history] if you need to revert to an older version.