Good day to you.
We have checked your reported query on prevent dragging a file during upload. By default, allowDragAndDrop of file manager component is set as false. There is no need to declare it in your application level. You can prevent the upload dragging by setting the dropArea of uploadObj in the FileManager as null using created () event.
Refer to the below code snippet.
<ejs-filemanager id='overview' #file [ajaxSettings]='ajaxSettings' [view]='view' (created)="created($event)">
this.file.element.querySelector(".e-control.e-uploader").ej2_instances.dropArea = null;
For your reference, we have prepared a sample.
Note: Upload functionality is prevented in online service, you can use the file manager local service in this link
Please let us know, if you have any concerns.