The trick to successfully separating the business logic from the mechanisms is to start with the business logic. Otherwise, if you write the data access (MongoDB, SQL Server, etc.) alongside the business logic, those two concerns will invariably end up intertwined. And then, it will seem as having been inevitable that the two were inseparable all along.

On the other hand, coding up the business logic in isolation of any of the mechanisms (web, database, event streaming tool, queues, and so on) is more likely to lead to success.

Why not try it out?