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!
An error occurred while saving the commentTammi commented
I went to the SharePoint backend site and for the channel I want to keep private I chose to "Manage Permissions" then removed read and edit permissions for the group team members, only allowing group owners to have access to the channel.