When you run a command like:
$ yarn global add create-react-app
Yarn is going to install any needed dependencies including any binaries. So, where is Yarn putting these binaries?
Let's ask:
$ yarn global bin
/Users/jbranchaud/.asdf/installs/nodejs/10.15.3/.npm/bin
This is where it is located on my machine. You'll want to run it on your own machine because the exact location will depend on the specifics of your installation.
See the docs for more details.