It just might be the case that you are accidentally making the new Audio Tracks within the Group Folder, hence the routing to the Group Folder and not Stereo Out.
When a new Group Folder track is made, it’s state is ‘open’ and ‘selected’, which means the next tracks that you make will be placed inside it. Please observe the Folder Open/Close status, it can be an easy miss especially if the folder is empty.
If you click on any other track or just close the Group folder, that’d mean the new tracks will not be placed inside of the Group Folder and it would be routed to Stereo Out. Please refer the video below.
Automatic routing is a feature of the new folder groups. When a new track is created inside such a folder it will automatically get routed to the folder’s group.
If you create tracks outside of a folder group I think Cubase will use the last setting from the “Add Track” dialog. This will be remembered for each track type individually.