Hi Viktor,
Thank you for contacting Syncfusion support.
We have checked your reported query and currently, we don’t have a built in option to remove/disable the ‘Add Group’ item in EJ2 QueryBuilder. However, we have prepared a sample level solution to achieve this requirement.
In that, we have faced an issue with the sample level solution. On further analysis, we confirmed this as a defect and logged a defect report. The fix for this issue will be included in our Essential Studio 2019 Volume 1 release which has been scheduled to be rolled out in the mid of March, 2019.
We will update you the sample once released, and we appreciate your patience until then.
Regards,
Silambarasan