Flat Shading/Flat Colors - Final Version - Illustrious

Use an Illustrious variant that has support for non-painterly artwork. Here's the one I use and recommend:

https://civitai.com/models/835655/illustrious-xl-personal-merge-noob-v-pred05-test-merge-updated

What is this?
This model generates pictures with little to no shading for a more natural, professional and believable look that doesn't feel too AI-sloppy.
It was trained under over 10 artists so it doesn't have a particular style, it should, in fact, work with pretty much anything!