Cross module communication in modular monolith

I have been learning about modular monolith project structure in this article: https://codewithmukesh.com/blog/modular-architecture-in-aspnet-core

Most of it makes sense to me but something I don't quite get is:

Cross Module communication can happen only via Interfaces/events/in-memory bus. Cross Module DB Writes should be kept minimal or avoided completely.

How exactly does that cross-module communication look?

Let's say I have 3 modules:

• Product
• User
• Security

My security module registers an endpoint for DisableUser. It's this endpoint's job to update a User and every Product associated with the user with a disabled status.

How does the Security module call User & Product update status method in a unit of work?

My understanding is that this pattern is intended to make it easier to extract a module to a microservice at a later date so I guess having it as a task of some sort makes it easier to change to a message broker but I am just not sure how this is supposed to look.

My example is obviously contrived, my main point is how do modules communicate together when read/writes are involved?