dbmanager: Can create and delete databases. A member of the dbmanager role that creates a database, becomes the owner of that database, which allows that user to connect to that database as the dbo user. The dbo user has all database permissions in the database. Members of the dbmanager role don't necessarily have permission to access databases that they don't own.
Reference:
https://docs.microsoft.com/en-us/sql/relational-databases/security/authentication-access/database-level-roles