IE11 is still among the most popular browsers in the world. Though Microsoft is promoting Edge Browser on Chromium engine. Many organizations have still not moved on to new offerings or taking their own time. Meanwhile, if you need to make your React Application compatible with IE11, check the steps below:

1. Create the app, follow this post, if not already done.
2. Add import 'react-app-polyfill/ie11'; as the first line in index.js file.
3. For common standard functions like Array.find() that are not supported in IE 11 add import 'react-app-polyfill/stable'. This should be the 2nd line in index.js file.
4. In package.json copy the production browserlist to development so you can test in IE11 and all other browsers that will work in production. Just add "ie 11" at the end of both production and development, browserlist section into package.json
5. Delete the node_modules/.cache directory.

//index.js file:
import "react-app-polyfill/ie11";
import "react-app-polyfill/stable";

//browsers list in package.json file in reference to #4:
"browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all",
      "IE 11"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version",
      "IE 11"
    ]
  }

If you are also using arrow functions so you’ll also need babel to update that for you. The babel-plugin-transform-arrow-functions is your best solution for this. Please check the documentation here.

you might still face some issues in your functionality like additional spaces added by Material UI date control which fails in IE11 but not other browsers. This might need to be taken care of individually on operations using that date value.