After my test on Gantt chart 2.2.3, I found that the tooltip page cannot be added. However,after the visual is created as follows, while hovering over a bar, the Start Date and the End Date are displayed automatically.
I also used Gantt chart-xViz to test, which can add tooltip page, but its display is a bit problematic. The start date and end date of the parent project it displays are wrong.
It is suggested that you contact the author of the custom view for help.