Not only can a monolithic code base be scaleable but you can make it into microservices by adjusting it's startup parameters:

    monolith --start-batch-jobs
    monolith --start-claim-processor
    monolith --start-graphql

And they would be interconnected probably via some clustering protocol with libraries that hide the complexity and runs a bus available in a litany of languages.

Need scale?

k8s replica count on the above pods.