typescript / .Net Core : downloaded jpg/png file format not supported

I'm having difficulty viewing downloaded png/jpg files, the file downloads properly but cannot be viewed. I think it could be related to the way I'm saving the object in typescript or something to do with content header types?

Backend: .Net Core 6.0 Web API

Frontend: Vue 3

This is the result of trying to open the downloaded image:

Fiddler trace shows the image being sent from the server:

This is how I'm downloading the file in TS:

await someService
.download(item.url, item.name)
.then(async (r: any) => {
  const blob = new Blob([r.data]);
  const link = document.createElement("a");
  link.href = URL.createObjectURL(blob);
  const disposition = r.request.getResponseHeader("Content-Disposition");
  if (disposition && disposition.indexOf("attachment") !== -1) {
    const filenameRegex = /filename[^;=\n]*=((['"]).*?\2|[^;\n]*)/;
    let matches = filenameRegex.exec(disposition);
    if (matches != null && matches[1]) {
      link.download = matches[1].replace(/['"]/g, "");
    }
  }
  link.click();
  URL.revokeObjectURL(link.href);
})
.catch((err: any) => {
  showError(err);
});

This is how the server sends its response:

public IActionResult DownloadAttachmentAsync([FromQuery] DownloadAttachmentInputDto model)
{
    try
    {
        FileStream fs = new FileStream(_pathToFile, FileMode.Open);
        return File(fs, "application/octet-stream", model.FileName);
    }
    catch (Exception err)
    {
        _errorHandler.Error(_loggedInUser, err);
        return BadRequest(_errorHandler.UserFriendlyErrorMessage(err));
    }
}

Request/response header?:

Not sure where else to look, any help is greatly appreciated!

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