Dear Miss_O224,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
From your description It seems you want to know how to restrict users from Creating a Document Library.
I have carefully read your query , I think is an option that may help you:
Assign Contribute permission to users, so that they may not add or delete lists or libraries in a site. Go to Permission setting page by Gear at top right of the page>Site Permission>Advanced permission settings, then select user and assign Contribute permission so that they may not create or delete lists/Libraries in a site.


Please remember to remove the previous permission user is granted. You may use Check Permission button to check what the user has in a site.
For more information, please check the articles:
SharePoint site permissions
Permission levels in SharePoint
Your understanding and patience will be highly appreciated.
If there is any misunderstanding, please feel free to correct me.
Have a nice day!
Best Regards,
Sophia