...
A new custom field named "Gantt Chart" will be created globally. Afterwards an automatic upgrade task will run to modify all your issues by setting value "show" into that new custom field "Gantt Chart". It's progress is displayed in steps of 10 issues within your JIRA log file. That's a necessary pre-requisite to display Gant-Chart as column on an issue page or search result page/navigator page etc. Without any value, a custom field will never be displayed, which is one of JIRA's native features. Finally, please add that new custom field to any screen you want to show.
Improved timeline (scroll horizontally, jump to today, zoom in/out via double-click on blue timeline or switch to another period of timeframe)
If you just want to scroll horizontally, please drag'n drop the blue scroll bar left or right:
...