I am creating a Gantt chart in New UX by using Start Date and End Date. Can I enter the text inside the bars of Gantt chart.
No, I don't believe so. But if it is something which is of great interest to you please share this as an idea on idea exchange forum here on community.
On Gantt you can Conditionally format your bars based on the logic. You can also conditionally format the milestones based on the logic. That might add some more info to the chart but it certainly will not allow you to input texts within bars.