Older browsers might be supported, depending on the React version you are using. React 18 dropped support for Internet Explorer, but you can keep using React 17 to overcome this.
Emotion, the companion dependency of React Awesome Reveal, currently supports older browsers, including Internet Explorer 11. However, this might change in future updates of the library.
In any case, the Intersection Observer API is not supported on older browsers, so you will need to polyfill it.
Polyfilling the Intersection Observer API
Then import it in your app:
If you are using Vite, Webpack, Parcel or any other modern bundler, you can also use dynamic import to load the polyfill only if needed. A basic implementation could look something like this: