Manger is a continuous accounting system.
At the end of each financial period consider “Close an accounting period” and “Set reporting period” in the old guides https://www2.manager.io/manager.pdf
Most entities such as inventory items and customers have an option to be marked as “Inactive” in their edit form. It doesn’t remove them from Manager, but it does move them to the end of their lists and prevents them from appearing in selection fields.