After create-react-native-app app2, I got lots of files without# # index.js in my project root file.Is this a bug?

It appears if you eject.
Before ejection the scripts know about your folder structure and will use App.js.
See package.json and app.json for how your app is configured and how it points to App.js, which is intentionally the entry point component of the project.
I solved!
Declaration of App is in package.json
./node_modules/react-native-scripts/build/bin/crna-entry.js
There, you can see App's default location which
var _App = require('../../../../App');
Then you can change it. I put it App.js in a src folder than it looks like this
var _App = require('../../../../src/App');
@cyb3rsalih worked for me, thanks!

For anyone coming across this: you shouldn't change files in node_modules, since they'll get overwritten when you update the package.
which i can do ? I want to hasve index.js
Most helpful comment
It appears if you eject.
Before ejection the scripts know about your folder structure and will use
App.js.