dropDatabase is not a privilege granted by readWrite all, the dbAdmin role will grant the necessary privilege. If dbAdmin grants more privileges than desired creating a custom role is another option.
https://www.mongodb.com/docs/manual/reference/built-in-roles/#mongodb-authrole-dbAdmin
https://www.mongodb.com/docs/atlas/mongodb-users-roles-and-privileges/#specific-privileges
https://www.mongodb.com/docs/atlas/security-add-mongodb-roles/#configure-custom-database-roles