In the columns attribute, I want to customize the columns. This time, I want to bind the event on the custom element.

Hello,
When you use the template function, you can only return HTML elements.
That means you can only add the Javascript handlers.

If you want to show native Vue or React components and add the native handlers, you need to use the onrender method:
https://docs.dhtmlx.com/gantt/desktop__specifying_columns.html#modifyingcellsafterrendering

Here are the demos:
https://files.dhtmlx.com/30d/bcac2d270e7cf8f74f9271d74ffc489b/reactive-gantt+gantt-instance+react-components.zip

https://files.dhtmlx.com/30d/025a888456a0f9ab7542a9ab631170cd/vue3+gantt_instance+vue_components-checkbox+grid_header.zip