First attempt (log output from expo eject):
Removed "main": "node_modules/expo/AppEntry.js" from package.json because we recommend using index.js as main instead.
But the real entry point was configured in app.config.js expo.entryPoint. So I commented out the (unsused) line in package.json, reverted and tried to eject again (log output):
expo.entryPoint is not needed and has been removed.
It was in fact not removed and the generated index.js did not reflect the configured app entry point.