Adding an Graphic to a Writer document, I can define the Anchor property via the context menu of the Graphic. But the "Graphic Frame" Styles does not allow to define the Anchor property.
This Option has to be added to the Frame Style Dialog !
It should be usefull to have same properties in both dialogs.
While this remains an outstanding enhancement request there is a workaround as described in the duplicate. Basically, edit the anchoring of a frame or graphic and then update the corresponding "Frame" or "Graphics" frame style to use this definition.
*** This bug has been marked as a duplicate of bug 32484 ***