Hi Michal,
Thank you for contacting Syncfusion support.
We have analyzed your requirement and attached image. In your sample there is no required space available between the Gantt schedule start point and taskbar for rendering the full taskName. So the task name values are adjusted based upon the space. But we can render the full task name at the beginning of the Gantt taskbar in GanttChart side by extending the scheduleStartDate value based on the required space. The scheduleStartDate property is used to specify the start date of the Gantt schedule.
We have prepared the sample for your reference please find the sample link below
Please let us know if you require further assistance on this.
Regards,
John R