How does this work?

This is how MultiRPC works.

MultiRPC does not modify your Discord client, user token or system to use the app and abides by the Discord terms of service.

The MultiRPC app uses a local connection (RPC) that communicates with the Discord desktop client that allows it to set your status for the logged in user account.

It works with all 3 Discord clients, Discord, Discord PTB and Discord canary. There is also an option in the app to specify what client to use.