If the future is already settled, does anything I do matter?
Yes. A history containing your decision is different from one in which that decision has no effect. In the essays' example, a region has one settled response for each specified boundary input. Change that input and its settled response can change. Uniqueness for a given input never means independence from the input. In a Sudoku, one completed grid obeys all its constraints; that fact does not mean changing a clue leaves the answer unchanged. Your deliberation, experiments and actions are among the world's actual dependencies. OPH's complete-history interpretation includes them in what makes the history consistent. It supplies no outside director who achieves the same outcome whatever you do. The practical conclusion is participation and responsibility, rather than permission to stop trying.
See also Do we have free will?, If reality is a fixed point, is everything predestined?
Also in Appendix A: Eighteen Questions.
This answer comes from OPH, Observer Patch Holography. OPH is a rigorous, consistent and complete description of the unified, self-creating computational Universe we inhabit. Its consistency is machine-checked: the fixed point at its core is constructed explicitly, and a theory with a model contains no contradiction.
To understand OPH and check every step yourself, start with the free book Reverse Engineering Reality. It builds the theory from the ground up, and the OPH Notebook answers your questions while you read.
read the free bookask the notebookor ask sage:read chapter 40: Does It Feel Like Anything, and What Is Left to Decide?watch a universe make its own particles