Detailed outlines help some people write clearly. For others (me included) they are more bother than they are worth.
If you don’t have a detailed outline, you still need a plan. At a bare minimum, you need to have a way of dividing your project into sections that will make sense for the people reading it. I call it a writing map.
A writing map is a list of the major points you want to make in the order you want to make them. And it includes what sources or other outside material you will use.
It divides the larger project into smaller segments that will be easier for your to write and easy for your reader to follow.
An outline or map can change (and probably will) as you work on your project. That’s a good thing, because it usually means you’ve found a better way to organize your project.