I am a discovery writer, I have been for many years, and I complete stories.
Scrap your outline.
Most discovery writers (including me) have struggled with what you are talking about; finding the climax, resolving the character arcs, dead-end "mysteries" that we could never figure out.
The solution to that is simple, but it is NOT outlining. For a discovery writer, outlining kills your characters. It turns them into machines that can't make decisions, and you feel you are forcing their emotions upon them.
I think you feel like you finished the story because you (as the author) have no more choice in how the story goes, your characters are no longer fluid, you are no longer excited to see what they will do, or what they will encounter. You have become a typist, instead of a story teller.
The solution to finishing books as a story teller is to have a logical conclusion for the story from the beginning. As an example, consider a film like Independence Day, which I did not write. The premise is aliens attack Earth, and we can't beat their tech. The final solution is we infect their systems with a computer virus, thereby defeating their tech, so our military can defeat them.
That is all a discovery writer should need to write the story, a main problem, and its solution. I do not consider this an outline, I consider it a direction to write in, and a provisional direction at that: If I think of a better ending, and I love it, I'll write toward that, even if I have to revise the book-so-far to some extent.
If while I am writing, my characters do something that would preclude that ending, I have to come up with a better ending right then, still consistent with what has happened, or within the realm of revision for what has happened. I don't want to rewrite ten chapters (although Stephen King, also a discovery writer, once scrapped something like a few hundred pages to save The Stand).
Revision is part of discovery writing, to create a coherent whole out of your wanderings. If character actions make the provisional ending illogical or dumb or impossible, then go back and find something else plausible for the characters to do that doesn't ruin the ending. Save a backup, in case you have lines you loved that might be re-used, but cut and start over. Or find a different ending that would work, a better ending, and revise what you need, throughout the book so far, so the better ending fits.
I do the same thing for a few other important "endings" in the book; I usually have a love story as a subplot in my books, a love story with an obstacle. I decide some provisional ending for that story too, a note on how their obstacle might be overcome, and they get together. If I introduce a mystery, I keep a note on how to solve it. I don't write any of the details, just a plausible notion of how it can be done; a direction to write in.
Scrap your outline. Put it aside, forget it, free your characters. Whatever you devised for the various endings, maybe keep them as notes, a direction to write in, but not too many of them.
Go back and let your characters be free, to make their choices in the moment like real people, to develop their plans on the fly, react and feel on the fly. Both villains and heroes. Let Jack be surprised when the present circumstances warrant surprise, don't try to force it on him. Where discovery writers shine is precisely that, what the characters do, say, think and feel seems organic and natural, it flows, because the writer has that moment in his head as he invents every line and action.
Sometimes I think of this as a football game; American version or European: The goal in every game is the same: You have to get from a starting point to the end of the field, against opposition. But the path to the goal is completely different every time. Different setbacks, mistakes and victories. No two games are ever the same.
Take your characters, and play a new game. Even if your final goal is the same, you don't have to get there exactly the same way as you outlined. Your outline found A story, one game. Screw up your outline with adversity, you can always add that: A fumbled ball is recovered by the opposition, a player falls and breaks an arm. It doesn't have to be a villain, it can be an environmental problem; a fire or storm or accident. A wild animal. They've run out of food and water. They encounter a mountain or river they can't cross, screwing up their timeline.
Kick your hero in the face and make yourself write a different game for them. Even if your note on how to resolve the main conflict stays exactly the same, let them react to different circumstances on the fly, make new plans. You need to give them new life so you are looking forward to seeing what they do when you sit down to write, and looking forward to figuring it out.