Hello Stacey,

When using the Kendo components with Bootstrap, Bootstrap modal dialogs prevent access to Kendo UI popups, which are opened by components placed inside the modal dialog. In such cases, use non-modal Bootstrap dialogs or modal Kendo UI Windows.

One option to resolve this is using the Kendo Window or Kendo Dialog components. The other is to prevent the focus of the bootstrap modal. We have a knowledgebase article demonstrating how to achieve this when using Bootstrap 3 and Bootstrap 4:

$('#testmodal').on('shown.bs.modal', function() {
          $(document).off('focusin.modal');
    });

For Bootstrap 5 the option I can suggest is to disable focus for the modal via the data-bs-focus="false" attribute or

 $('#testmodal').on('shown.bs.modal', function() {
          $(document).off('focusin.bs.modal');
    });

Regards,
Nikolay
Progress Telerik

Hello Dmytro,

Could you please provide more details about the scenario and the requirements? I will appreciate it if you could specify the widgets to which you need the popup.appendTo option to be included. Currently popup.appendTo option is available for the input editors such as - DropDownList, ComboBox, MultiSelect, etc. Before approving the request it will be helpful to have more details about the exact requirements and the component which you think needs to be extended. 

Regards,
Neli
Progress Telerik