As a Roblox developer, it is currently too hard to have channel tab UI to switch between channels in the new TextChatService. The legacy Chat service provided the players with a tab at the top of the chat window to switch between channels. This is not possible with the new service unless the developer manually creates a system to let the player have control over which channel they are speaking in.
The legacy chat had several settings to customize chat channels:
UI for switching text channels was mentioned in the TextChatService DevForum post last year, but there have been no updates: TextChatService is now the default for new experiences! - #116 by SubtleShuttle
