There are various context menus for different elements on the Gantt chart. You can access these menus by right clicking on the associated element.
Grid header context menu
Right click on the grid header (top row) to show columns and filtering options.
Timeline header context menu
Right click on the timeline header to adjust how you want to display the timeline view.
Task context menu
The task context menu is only accessible in edit mode.
Right click on a task row to show operations related to task management.