Do use focusNode.requestFocus(). It is not necessary to call
FocusScope.of(context).requestFocus(focusNode). The
focusNode.requestFocus() method is  equivalent and more performant.

Unfocusing

UnfocusDisposition.scope and

The previouslyFocusedChild disposition will search the scope to find the
previously focused child and request focus on it. If there is no previously
focused child, it is equivalent to scope.

Focus widget

The Focus widget owns and manages a focus node, and is the workhorse of the
focus system.  It manages the attaching and detaching of the focus node it owns
from the focus tree, manages the attributes and callbacks of the focus node, and
has static functions to enable discovery of focus nodes attached to the widget
tree.