Hi Karol,
Greetings from syncfusion support
Based on your requirement we have prepared a sample and tried to reproduce the reported problem. But after choosing the dates from date columns the Grid display as defined format. Its working fine from our end. Please refer the below sample for more information.
If you still face the issue, please share the below details that will be helpful for us to provide better solution
1) Please share your datasource ,we would like to see on which format you have defined the date for the dateColumn.
2) If possible, replicate the issue with our above attached sample.
Regards,
Rajapandi R