Comes to broken link?

I try to upload from my GitHub an React-app, but when I try it I come to broken link? Its no router in the app…just small app?
Here is the link to my GitHub-app:

Here is the link to the netlify-app:

Please help me to understand

Best regards

@Kaj What do you have set for your Basic build settings?

Your build throws warnings which will be treated as errors unless you set CI to false, so…

Your Build command should be CI= npm run build
Your Publish directory should be build