React19 dropped UMD to make the testing and release process easier for Meta. It's a weird reason as the whole building process is a whopping one JS script with about ~100 lines of code..

So I've taken it upon myself to bring the UMD glory of React back, enter UMD-React. This GitHub repository checks for a new stable release of React on NPM daily via a Workflow and if detected, fetches the new version, builds, and publishes the latest release on NPM.

Unless some major changes happen, this is zero-maintenance, always up-to-date UMD version of React available for anyone who needs it.
Cheers! Consider starring the repository if you find it helpful, Unpkg links are included: https://github.com/lofcz/umd-react ⭐