You have to set the datagrid to either single selection or multi-select. You cannot change this per button.
I would advise to set the datagrid to multiselect, to accommodate your new button.
Then change the microflows that the other buttons start, so that you can give a list as parameter.
In this microflow you can then count the items on this list and if there is only one, you pass this to the edit/ delete page.
If there is more then 1 object, you can show a message to the user indicating that only one object at a time can be edited/ deleted.
Hope this helps!