Add leaderboards to an app version - Configure Game Center - App Store Connect - Help - Apple Developer

Leaderboards can be added to your app version once configured. For information, view Configure leaderboards.

Configure leaderboards and achievements - Configure Game Center - App Store Connect - Help - Apple Developer

Integrate Game Center Leaderboard Using Game Kit Framework in iOS 7

Using Google Play Services Leaderboards in Unreal Engine Projects

Game Center Overview - Apple Developer

Game Center is getting an update! : r/ios

Game Center arrives on the Mac via Mountain Lion, but where are the games? - CNET

Add multiplayer compatibility - Configure Game Center - App Store Connect - Help - Apple Developer

app store - iOS App submission is rejected as using Game Centre Leaderboards and Achievements but has not submitted for review - Stack Overflow

Add a Leaderboard to Your iOS Apps, by Julie Elise

Apple Game Frameworks and Technologies: Build 2D Games with SpriteKit & Swift by Tammy Coron

Configure leaderboard sets - Configure Game Center - App Store Connect - Help - Apple Developer

Game Center and Leaderboards for Your iOS App