We had to disable the viewer for datasets with a script for now, because some people were abusing it. Sorry for the inconvenience.
We’re seeing if there is a viable long-term solution.
In the meantime, if you want the dataset viewer to work you need to remove the dataset script and use a supported data format (csv, parquet, etc.) Personnally I’d recommend uploading the dataset using the datasets library and push_to_hub().