I copied the code as shown in the your video but the player is always disconnected. Each additional game window I launch always only shows 1 player. In other words your extension doesn't work.
Viewing post in Online Multiplayer Extension for GDevelop comments
This issue has been reported as resolved.
https://pandako.itch.io/ome4gd/devlog/544229/v-007
astasio
I updated the ISRG certificate and the error resolved. It was just a mac os update problem