Asim, we have logged a feature request for your
requirement to provide support for custom dialog modal. You can track the
status of the feature from the feedback link given below.
Feedback: https://www.syncfusion.com/feedback/41440/need-to-provide-support-for-custom-dialog-modal-in-gantt-chart
As we have already lined up some major features, we could not
implement this support immediately. We will implement this and include it in
any of our upcoming releases. Please cast your vote on this feature. Based on
the customer demand we will prioritize the features in our upcoming road map.