by Lisa Kidder.
David,
There are many good things about the new grading interface, especially for annotating PDFs, but I agree that it would be nice to be able to turn off the blank block taking up so much screen real estate.
I did notice in the dev notes (https://docs.moodle.org/dev/Assignment_Grading_UX) there were/are plans to make the interface flexible and re-configurable, but that has not yet happened.
With offline assignments, the option to switch back to the old grading interface, or an interface that completely hides the PDF Annotation screen seems very logical.