I made a ticket on this but thought I would post here as well.
It appears there is an issue with the latest Telerik Blazor version when it comes to adding new grid items.
I can't get it to work in my project and can't get it to work in your demo either.
https://demos.telerik.com/blazor-ui/grid/editing-inline
Click add new employee.
Fill the info boxes.
View the added row. The Name field is empty.
I stepped through the code in my project and the parameter from the field is always null.