Hi Aks26,
disabled property should disable the element but there seems to be an issue with it that will be fixed in the next release. May I suggest adding the following CSS to accomplish the same result in disabling user interaction for the component:

smart-gantt-chart {
    cursor: default;
    pointer-events: none;

You can specify the CSS selector to work only when adding the disabled attribute or something else (smart-gantt-chart[attribute-name]).
Furthermore, you can disable resizing or dragging for individual tasks via the disableResize/disableDrag attributes. You can do that in the task definition in dataSource or dynamically via the updateTask method. Here’s a demo
Best Regards,
Smart HTML Elements Team