https://superfriendly.com/design-systems/articles/folly-of-design-system-foundations/
The most important difference between a style guide and a design system is their approaches to the idea of change. Most style guides try to limit change. Design systems lay the groundwork for change to happen easily, elegantly, and scalably. Design systems are at their most valuable at the moment of change.
While the best style guides allow you to create within the rules, most only succeed at enforcing consistency by censuring and eliminating unwanted variation. Useful, but restraining.
Design systems instead should be a collection of processes. The best ones focus more on what you can do and give you the tools to do it.