Problem with XLS export

[Angelina]

Hello!
I use HTML5Viewer with Telerik.Reporting.Trial and  I can't see XLS export options in viewer.

As far as I now XLS format not need third-party libraries (like OpenXML), but I installed this libraries too and add assembly redirect. It is not working.
Then I try add option programmatically in GetDocumentFormats() override method in my controller and I can see XLS option, but report return error "XLS rendering format is not available".
I readed article "Missing DOCX, XLSX, PPTX, XPS export options in viewers or "X rendering format is not available" error message", but this recommendations not help me.
Can you help me?
My JSON configuration for extention:

"extensions": [
  {
    "name": "XLS",
    "description": "XLS",
    "visible": "true"
  }
]

[Neli]

Hello Angelina,

We will bring back the XLS format for .NET Core in some of the upcoming releases and we will limit the rendering extension only to the Windows environment.

Because the old Excel rendering uses unmanaged code that can work only on Windows and it has a better alternative that is 'XLSX', we had decided to removed it from .NET Core, as we would like our Reporting solution for .NET Core to be cross-platform and behave as close as possible on all platforms.

Let us know if you have any questions.

Regards,
Neli
Progress Telerik