What is the structure of MVVM in WPF?

Question

WPF

I am getting acquainted with the MVVM design partner when writing a WPF application, and no matter how much I searched, I really did not find unambiguous information about where to put the logic of interaction with the database. I understand that the implementation of MVVM may differ, and I think that there is no one right solution, but how can I do it better? I use Entity Framework Core in my application, the application structure is shown on the screenshot. Now I have a data context class and a class that contains methods for interacting with the database (add, delete, get, etc.) placed in the Database directory. Is this the right decision, or should I do something else? And more about the ViewModel, do I understand correctly that the ViewModel should not be alone, and each model and view should have an intermediary in the face of the ViewModel?