BubbleChatEnabled
If true, entering a message in the chat will result in a chat bubble popping up above the player’s Player/Character. This behavior can either be enabled by directly ticking this checkbox in Studio, or by using a LocalScript:
local ChatService = game:GetService("Chat")
ChatService.BubbleChatEnabled = true
This must be done on the client, toggling this value in a server-side Script will have no effect.