The last way to join a specific Roblox game is if players have friends playing in that server. They are able to join any friend's game if they have the "Join In-game" setting enabled.

Earlier this year, however, a new function was added called Roblox Connect, functioning as a video chat interface of sorts that lets friends call each other as their own in-game avatars.

How to Enable Voice Chat and Call Someone in Roblox Unfortunately, Roblox Connect isn’t available to everyone due to an age limit.