How is the senior week calculated in Simployer, does it need to be entered manually, or will the employee receive the extra vacation days automatically?

This is automatically calculated based on what you have entered in system settings. To view the settings, go to the menu on the left -> System Settings -> Vacation. There you will find an option called 'Extra vacation days for older employees.' By default, this is set to 5 days, but if you have a different practice, it can be adjusted here. For the 'Minimum age for extra vacation days,' you can enter the age at which the extra vacation days will be calculated.