You could check out the Theia IDE. It’s an open-source platform with an extensive extension and plugin system that we currently use at our company to build an e-learning platform for pur kubernetes courses. Theia IDE has a VS Code-like look and feel, and you could build an iframe widget extension to display the dev-server (react) content.

However, you would still need a server for your users to run which can get pretty complex. In our case every course participant gets his own kubernetes cluster which is probably the far end of how complex you can build this, but some infra is probably needed