Yes, It was ArcGIS SDK for JS. I tried with the KMLLayer Class but it was not working when we create it from the upload file. Creating a URL from the Blob and adding it to the KMLLayer Class.
The KMLLayer doesn't parse KML via the client, it sends the KML url to a utility service that parses it into features and returns those results, so passing a KML blob won't work. The KML url has to be accessible by the utility service.
Per the documentation. https://developers.arcgis.com/javascript/latest/api-reference/esri-layers-KMLLayer.html
The KMLLayer uses a utility service from ArcGIS.com, therefore your kml/kmz files must be publicly accessible on the internet.
Thanks Rene for your help here 😊.
BTW: sorry I tried to move the whole thread to this forum but apparently I did it wrong ^_^''.
Just in case, and for context, this is the original question.