Yes, you're not alone—several Mac users have reported that the new Microsoft Teams client (Teams 2.0) currently lacks the “Add channel” option when scheduling meetings.
You may switch over to Team Web App: https://teams.microsoft.com
The browser version often retains full functionality...
Else, if you have the Teams add-in for Outlook, you can schedule a Teams channel meeting there by selecting the correct Team/channel under “Location”.