How can I block users from creating SharePoint sites from Teams, O365 Groups and all other sources?

Hi @Robert Peeples

As above said, you could try to follow these steps to block users from creating SharePoint sites from Team:

1. Go to the SharePoint admin center.
2. Click on "settings" in the left-hand menu.
3. Scroll down to the "Site Creation" section.
4. Choose the option "Only users with permission can create sites" and select the appropriate permission level.
5. Click "OK" to save the changes.

To be noticed that this setting doesn't affect whether users can create teams or Microsoft 365 groups and their connected sites.

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You can restrict users from creating SharePoint sites by following these steps:

1. As a Global Administrator or SharePoint Administrator in Microsoft 365, you can let your users create and administer their own SharePoint sites, determine what kind of sites they can create, and specify the location of the sites. By default, users can create communication sites and Microsoft 365 group-connected team sites. Note that disabling site creation for users does not remove their ability to create Microsoft 365 groups or resources, such as Microsoft Teams, which rely on a group¹.
2. Go to Settings in the SharePoint admin center, and sign in with an account that has admin permissions for your organization. Select Site creation. The Site creation page appears. If you want users to be able to create sites from these services, select Show the options to create a site in SharePoint and create a shared library from OneDrive. Note that even if you clear this checkbox, users may be able to create Microsoft 365 groups from other places in Microsoft 365. Each group always comes with a team site. Learn how to manage who can create Microsoft 365 groups¹.
3. Admins in the SharePoint admin center can choose to either enable or disable subsite creation across sites or enable for classic sites only. When subsite creation is being disabled, not only will the subsite option be hidden from the command bar including classic, but also users won’t be able to create new subsites directly through a URL or API¹.

By changing the global Teams settings in the Microsoft 365 admin area, Teams can indeed be prevented from building a SharePoint site².