Sharepoint list mirroring

Hi Michal_Tyl, 
Thank you for reaching out to the Microsoft Fabric Community Forum.

The issue occurs because SharePoint User/Group fields such as Created By and Modified By are stored as complex nested objects instead of simple text values. These fields contain multiple properties like Display Name, Email, Claims ID, and other metadata. Currently, the mirroring process in Microsoft Fabric mainly supports standard scalar data types, so these nested User/Group columns are skipped instead of being automatically flattened into readable values.

As a workaround, you can create additional text/calculated columns in the SharePoint list to store simple values such as the user’s Display Name or Email, which will mirror correctly. Alternatively, after mirroring, you can use Dataflow Gen2, Pipelines, Notebooks, or SQL/Spark transformations in Fabric to expand and flatten the nested User/Group structure manually. Currently, this behaviour is considered a limitation rather than an issue with your SharePoint list configuration.

Please refer these following links:
1. https://learn.microsoft.com/en-us/fabric/mirroring/sharepoint-list? 
2. https://learn.microsoft.com/en-us/fabric/mirroring/overview? 
3. https://learn.microsoft.com/en-us/fabric/mirroring/sharepoint-list-tutorial? 

Hope this helps. If you have any questions regarding this, please feel free to reach out us. We will be happy to help.