Unable to refresh dataset with Column content exceeding 315 characters

Hi pallavi_r ,

Thank you for reaching out to the Microsoft Fabric Community with your query.  The solution provided by the lbendlin & Poojara_D12 is accurate. Here are some additional points to consider.

•  Ensure that the column type in the source system (SharePoint list) is set to allow for longer text entries. If   it's a single line of text, consider changing it to a multiline text field.
•  If the file names are consistently exceeding the character limit, consider using Power Query   transformations like Text.Middle() or Text.Start() to split or truncate the text safely before loading.

For more detailed guidance, you can also refer to the following resources, which might be helpful for you.

Link:  How to increase Character Limit for Multiline Text Field in SharePoint - Microsoft Community.

If my answer addressed your query, kindly mark it as the Accepted Solution to assist others.

I'd also be grateful for a 'Kudos' if you found my response useful.