Binary search works on any monotonic search space, not just sorted arrays. If you can define a condition that's false for all values below some threshold and true for all values above (or vice versa), you can binary search.
"Find minimum capacity to ship packages in days" doesn't look like binary search. But the answer lies in a range, and for any capacity , you can check if it's enough. Below the answer, shipping fails. At or above, it succeeds. That's a monotonic condition.
When you see "find minimum/maximum value that satisfies X," think binary search on the answer space.