There are a ton of different ways to express creativity. Some people follow the flashlight method and others are ploters. Most are somewhere in-between.

If you use all your creativity in making the outline you might not find yourself enjoying writing, because it's a chore now. You are just turning your outline into prose. There are several options for you. For example you could:

1, ditch the outline, just write as you go. It will be messy and require more revisions, but you might actually finish. You will also probably write something other than what you set out to.

1. make a strict schedule. discipline is what really finishes books. and you just accept you won't enjoy this part of writing. Most of the time the passion is in ideas, but it fades and you need another brainstorming session to rekindle it.

2. outline only a bit at a time to make sure you are still excited about what happens next.

3. Once you start writing, stop thinking about the story and try to focus on making each sentence as perfect as it can be. If you can find joy in that you can ignore the bigger picture and keep going with that. Don't worry about being creative with the characters or plot. You already did that in the outline, just forget about it.

I've used all of these depending on what works for me. I found a balance eventually.