There's a huge range between monolith and microservice approach, and even a monolith will have dependent services. A simple web stack these days might include nginx, a database, a caching layer, some sort of task broker and then the 'monolith' web app itself. All of that can be sanely managed in k8s.
Right... IMO monolith is better understood as a reference to the data model than deployment topology. If you only have a single source of truth, then your application is naturally going to trend towards doing most of its business logic in one place. This still doesn't displace the need for other services like caching, async tasks, etc., that you identify.
I definitely wouldn’t be managing my own database or caching layer without a very good reason. I would use a managed service if I were using a cloud provider.
