Hi Marko,
Thank you for contacting Syncfusion support.
We have analyzed your requirement and screenshots. Currently in Gantt there is no support to search the parent records and we can only search the least child records. If we search the least child records, then the corresponding parent records are also get displayed in Gantt. Can you please share the importance of this support in your application? It will be helpful for us to consider this feature and prioritize in our upcoming volume release.
Please let us know if you require further assistance on this.
Regards,
John R