Which outline format is most effective for a beginner writer to write a fiction novel?

The one that works for them.

Let’s say I were to give you any answer, and it was objectively correct and objectively the best format to work with.

If you hate it and don’t want to use it, what good is it to you?

For example, I used to use what we used in school:

(title)

I. Section 1

Introduction

Part after intro

Blah

Blah blah

I. Section 2

Start of approach to mid point

Part after that

And so on until you reach the end, regardless of how many sections there are and etc.

But maybe that’s not what works for you.

Maybe you’re looking at that and wondering why the fuck I use Roman Numerals, regular numbers, then small letters. Maybe you prefer visual stuff. Maybe you prefer using a program like Scrivener or Plottr to assemble your outline. Maybe you like working with an actual physical outline, like on a real life corkboard.

Feel free to use any idea for an outline to start, whether it’s the best one, something like what I suggested, or something else.

Find out what works for you through experimentation.

Then use what works best for you.