Google
It's a long time coming, but Google has finally given Stadia users the ability to join multiplayer games without needing an invite. The feature is already live on Far Cry 6, so you can invite friends to join you without having to dig into the menus and issue an invite.
Google says the feature is available on "select games" and disabled by default, but The Verge and 9to5Google pointed out it is enabled by default. It works on the Stadia app for Android and the web version that runs on iOS.