Until now, when you wanted to create a new channel, you had first to access the Teams where you want to create the channel.
Well, good news as now you can do it directly from the top level (the + sign shown on top of all your Teams).
When creating the channel from the top level, you have then to select the Teams where the channel will be created as well the channel type.
The corresponding update is currently being deployed for Targeted release while the deployment for Standard release is expected to start mid-February with a completion expected by late February.