Hi @Hugo Leung,
Thank you for reaching out to Microsoft Q&A forum!
I would like to inform you that currently, the designer only supports preview outputs that are stored in Azure blob storage. If your data is not stored in Azure blob storage, you won't be able to preview it in the designer canvas. Since the Azure ML sample data is not stored in Azure blob storage, it's not possible to preview it in the designer canvas.
To repro this issue, I uploaded the data to Azure storage and was able to preview the data output in the designer:
For more info see: Limitations.
Also see: Create and manage data assets.
Let me know if you have any further queries and I will be happy to assist.
If this answers your query, do click Accept Answer
and Yes
for was this answer helpful.