This article applies to all TeamViewer users.
In case you are chatting with a person using an older version of TeamViewer, you will receive a compatibility mode notice within the TeamViewer.
As a result, some advanced features are not supported for these chats, eg. indicators for whether a message was read or if the other person is typing at the moment.
When you are chatting in this mode, "compatibility mode" is displayed directly under the name of your chat partner.