create-react-app, installation error ("command not found")

You are able to apply the following solution:

$ npm config set prefix /usr/local
$ sudo npm install -g create-react-app
$ create-react-app my-app

The environment variables are not set properly. When you run the create-react-app it shows you a path along with the error. Copy that path and add it in the environment variable.

Alternatively you can use the command:

npx create-react-app <app_name>.

This will do the work for you.