React tab doesn't appear in chrome developer tools

You can't see React tab because, Facebook have updated React DevTools to have Components and Profiler Tabs. ⚛️ Components tab serves same purpose as React tab in older versions. From description,

You will get two new tabs in your Chrome DevTools: "⚛️ Components" and "⚛️ Profiler".

The Components tab shows you the root React components that were rendered on the page, as well as the subcomponents that they ended up rendering.

This can be seen from version 4.0.0. See the release notes here

After installing the extension, you will have a little 'atom-like- react icon next to your extensions (usually top right part of the screen) and if a website wasn't built with ReactJS, this extension sign will be grayed-out and there would be no menu in DevTools. However, I would recommend trying updating GoogleChrome and reinstalling the extension. Sometimes the restart of the computer will help.