I am using v6.0.0-beta.2 and this is the working solution for me:

`        const mockFile = {
                    name: asset.name,
                    id: asset.id,
                    accepted:true //this is required to set maxFiles count automatically
                };
                mydropzone.files.push(mockFile);
                mydropzone.displayExistingFile(mockFile, asset.url);`