This is happening because when you group by this column, the datasource does not know how to handle grouping for such complex field, sadly we support grouping only for base properties such as "string", "number", "date" "bool".
See the difference if you bind the column to the Category.CategoryName
The updating won't work properly because it will only update the Category.CategoryName
filed not the whole Category
object. So there is not really universal solution when using nested object, instead I would suggest using the foreignKey column approach. Grouping and updating is working as expected there:
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