I notice now that you are talking about a summary row, not the DataGrid footer.
If that is the case, then you are doing the right thing: add one row at the end of the list of dictionaries.
You can add some logic to the template form, for example to make the last row bold. If I remember correctly, that’s what I did in the DataGridJson. On the first example on this demo page you can see the result. (And I realize now that I left the Delete button on the summary row of that demo… I will fix that)