This feature item is still in the works. We will keep you posted as we have new info from the feature team.
Currently we have Teams defaulted to show you the first (up to five) channels ever created. If you want to add more channels to your left rail view, just click the ellipses next to the channel name and select “Favorite”. When you favorite the channel, it will then be “pinned” to your left rail under that team name.
Try that and let me know if that meets your needs!
This feature is still being reviewed by the feature team. No decision has been made yet. I’ll keep you posted.
We’re currently working on defining a compact mode experience. I will post more details when we have more to share.