Hi Stefaan,
Thanks for contacting Syncfusion support.
We have checked your query and based on your requirement you have to set the IdUser property is List<UsersTable> and you have to define the display values of that column by writing a converter for DisplayBinding. Please refer the below UG link for DisplayBinding Converter.
Query regarding integer-value to be converted to an enum-string
You can achieve your requirement by writing the Converter of the GridColumn.DisplayBinding to customize the cell content.
If your requirement is defer for this, could you please share your sample along with replication procedure, that would be more helpful for further analyze.
Regards,
Ashok