I thought this was fixed in a previous release, but null dates display as 1/1/1970 on data grids.
This issue has indeed been fixed some time ago and local tests show that NULL dates are not displayed in a data grid component with the latest Radzen version.
Could you please check if there is a node_modules directory within the \client\ directory of your Radzen app? If there is you can try deleting it and rebuilding.
That did solve it, thankS