Maybe it's just a me problem, maybe I need to be more disciplined. Not sure but it catches me quite often.
One technique I use when I find that happening is to check out a clean branch, and first make whatever structural change I need to avoid that rabbit hole. That PR is easy to review, because it doesn't change any behavior and there are tests that verify none of my shuffling things around changed how the software behaves (if those tests don't exist, I add them first as their own PR).
Once I've made the change I need to make easy, then the PR for the actual change is easy to review and understand. Which also means the code will be easy to understand when someone reads it down the line. And the test changes in that PR capture exactly how the behavior of the system is changed by the code change.
This skill of how to take big projects and turn them into a series of smaller logical steps is hard. It's not one that gets taught in college. But it lets us grow even large, complex code bases that do complex tasks without getting overwhelmed or lost or tangled up.
Maybe there's a partial solution if I can keep those commits clean and separate in the tree. And then when I'm done reorder things such that those all happen as a block of contiguous commits.