The built-in Add button on the grid toolbar puts a row at the top of the grid, but this model is not yet in the data source the grid is bound to. Once the user clicks the Save command column button, you get the Create event, so you can add the new model to the grid data source - you can do that at the end (List<T>.Add(myNewModel)), or at the top (List<T>.Insert(0, myNewModel)).
I was under the impression that you didn't want the built-in Add and Save buttons from the grid, which is why I suggested implementing the insertion of a new record separately. You can still invoke it from a button on the grid toolbar, though, just use a command name that is different from "Add" so you can handle it as a custom command that does not invoke the built-in row addition.
There must be some form of an Add/Insert New Item button, because the grid can't otherwise know to add this blank row.
If I am misunderstanding something or you need some more details, just let me know.
UI for Blazor