Hi @Sally Garforth,
Thank you for reaching out to Microsoft Q&A!
If I understand right: Yes, it is possible to set up multiple sub-sections in the Content Library of a Class Notebook in Microsoft Teams. You can do this by using Section Groups in OneNote (desktop app), which allows you to create a hierarchical structure like this:
By design, you can preview and make any edits to the sections that will appear in each student's private space in their Class Notebooks. There are default sections that you can remove or edit. Select + Add section to add additional sections.
For more details, please check this reference: Set up a Class Notebook in Teams using existing content - Microsoft Support
Feel free to contact me if there are any misunderstanding on this situation, I'm here to help you further if needed.
Best Regards
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