As above said, you could try to follow these steps to block users from creating SharePoint sites from Team:
- Go to the SharePoint admin center.
- Click on "settings" in the left-hand menu.
- Scroll down to the "Site Creation" section.
- Choose the option "Only users with permission can create sites" and select the appropriate permission level.
- 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.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.