Views available in threads
You can view a thread in 3 convenient ways.
Collapsed view:
In a channel, by default you will see your threads in this view. The lead thread message and the recent unread messages will be available in this view.
Expanded view:
Clicking on the View all replies will open the thread, you will be able to view all the messages in the thread from this view.
Split view
Clicking on Open as new chat will open the thread as a new chat.
You can leverage this view to be simultaneously informed about the current conversations in the channel as well as open the thread as a new chat and reply in the split view.