I don't want 100 different SharePoint sites. How to create private teams w/o a new site?

There is no supported way to create a Microsoft Team without creating a SharePoint site.

There is also no supported way to create a Private Channel without creating a separate SharePoint site.

There is also no supported way to have “multiple private areas” inside a single SharePoint site that map to Teams channels.

This is the product architecture.

If each group/project doesn’t need its own Planner, Notebook, mailbox, or private channel, then 

1. Create ONE Team
This becomes the “container” for everyone.
(e.g., “Operations” or “Projects”)

2. Inside that Team, Create all standard channels 
Each channel = one project.

3. In SharePoint, go to the “Documents” library
Each standard channel = a folder. Teams will automatically create one folder per channel in the SharePoint “Documents” library.

4. In the backend SharePoint site, create MORE structure if needed

You can create:

• Multiple document libraries (one per group/project)
• OR Folders with broken inheritance

Each one can have its own permissions.

5. Break permission inheritance on each channel folder, assign custom permission
For each library/folder:

• Remove inherited permissions
• Add the correct SharePoint groups
• Give each group the right access (Read / Edit / Contribute)

This gives each project a private document space without creating new SharePoint sites.

6. Add each document library to Teams navigation

You can surface these libraries inside Teams using:

• Tabs in any channel
• SharePoint links in the left navigation
• Pinned links in the Team
• In Teams > Shared > Add Document Library to add link of any document library

Note: 
Files stored in the secured folder
Chat stays in the channel (not private)
Tabs can point to project-specific pages/lists

This option gives each group a clean, private document space without creating new SharePoint sites. This is the closest thing to “private channels without new sites” that Microsoft allows.

This method does NOT give you:

• Private channel chat
• Private channel membership
• Private channel Planner
• Private channel OneNote