WOW Scores a new website that allow you to integrate a leaderboards on your GDevelop 5 game.
It’s free and you only need to register to start reading the documentation and integrate the GDevelop JSON API in your game.
Visit wowscores now.
Also you can check a working demo game of the WOW Scores API potential
Take a look here

It’s super easy to integrate leaderboards into your games with the help of this API, you are going to be able to add players to your game, even with an auth system for your player to login into the game.

Add the POST request with the help of the actions in GDevelop 5, then retrieve the API server Data to your game and act in kind.