Thanks for your update.
We have analyzed your query , We regret to inform you that currently we don’t have a support for “Applying validation rules in SfDataGrid”. We have already logged this requirement as feature request in our database. We don’t have any immediate plans to implement this feature. At the planning stage for every release cycle, we review all open features and identify features for implementation based on specific parameters including product vision, technological feasibility, and customer interest. We will implement this feature in any of our upcoming release. We will let you know when this feature is implemented. We appreciate your patience until then
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Also as mentioned in our previous update, You can use custom validation using CurrentCellValidating and RowValidating events or you can use built in validation using IDataErrorInfo/InNotifyDataErrorInfo instead of ValidationRule.
Please refer the below UG link for IDataErrorInfo.