From your following comments I see that you consider a monolith a software that does "everything", from managing staff holidays to giving services to customers.

From your following comments I see that you consider a monolith a software that does "everything", from managing staff holidays to giving services to customers. But this isn't what monolithic architecture Vs microservices is about; if you have independent business processes, it's been completely normal forever to have independent "monoliths" to manage them. Many proponents of microservices though request that you split your software into small independent services even when they manage the same business process, and this is where the complications come.