When/where/if:
1. Illustrations should be used.
2. Photos should be used.
3. IxD (interaction design) / animations.
4. Colour palette selection / creation.
5. Flourishes.
These are the things I struggle with when designing generic corporate marking websites. I'm not a designer but I've worn the designer hat many times. I always warn my employer/client that I'm more of a technical designer than a creative one. Nowadays I just stick to application design since it's 100% technical.
Example: as someone who's more technical than creative I could have come up with the overall layout of the Excalidraw+[0] website but I don't think I would have thought about adding circles around keywords or the dashed line that leads users down the page.
Playfulness, "flair" and other emotive forces guide creative decisions usually, but there's nothing stopping a technical person from arriving at similar outcomes via a more technical process. It will take more time and be less fun, less satisfying, but it's possible.
For example, once the basic IA is worked out, you could have a phase of the project called "flourishes", where your knowledge of illustrative techniques, eye-tracking, colour theory and UX tricks and so on, guides the design. Along with business needs, communication preferences... Another phase could be "product photography" where knowledge of what makes a good photograph comes into play.
But yeh it's usually easier to get a professional designer who enjoys and does these things all day long!
Can you provide an example of a 20% creative decision that has no technical aspects?