JSX compilation may not be compatible with React 19

**Do you want to request a *feature* or report a *bug*?**

Kind of a grey area. Not a bug _yet_, but it may be within 6 months. Depends on the final React 19 implementation.

**What is the current behavior?**

JSX is compiled into React.createElement

**What is the expected behavior?**

JSX is compiled into `_jsx` function where: `import {jsx as _jsx} from 'react/jsx-runtime';`

https://legacy.reactjs.org/blog/2020/09/22/introducing-the-new-jsx-transform.html

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

React 19, supposedly according to this documentation: https://react.dev/blog/2024/04/25/react-19-upgrade-guide#installing. However, the current release candidate doesn't appear to be creating these console errors yet. This JSX transform has been available since React 17, so there shouldn't be many apps still reliant on React 16.

Start by locating the TypeScript JSX compilation entry point and reproducing the current React.createElement output. Compare it with the React 17+ automatic JSX transform using react/jsx-runtime; done means JSX compiles to the _jsx import form while existing behavior remains supported.

Written by the indexing model from the issue text.