What is the meaning of this error/why does it happen?

• there's a dependency issue between react and react-scripts. the react version you're using is 19.0.0-rc, a release candidate (which might introduce breaking changes). though, react-scripts is asking for a version react version 16 or higher. the current version you're using being a release candidate may be the reason the issue occurs.

How do I resolve it (without causing some other problem).

• Downgrade react
• Or solve the bigger issue which is react-scripts is low key depreciated. React recommends you start react through a framework -- i.e. vite/ nextjs/ etc:

You can definitely use React without a framework—that’s how you’d use React for a part of your page. However, if you’re building a new app or a site fully with React, we recommend using a framework.