It means other parts of the economy must shrink. Population is no longer increasing which means every percentage of growth in one sector is offset by losses in another. There are only finitely many people and each person can only be in one sector at a time vs the previous regime where population growth meant every sector could grow concurrently by hiring from a growing population.

Modern capitalism requires an infinite supply of people to maintain economic growth. The model is entirely busted because it is at odds with physical constraints and dynamics of a finite planet. I personally consider the whole thing a collective delusion because infinite growth on a finite planet is a logical and physical impossibility. Unless everyone decides to live in VR where nothing matters then the economic models must at some point make a connection with reality and at that point it becomes obvious that the capitalist model of infinite growth is untenable unless there is a supply of people growing at a faster rate than whatever economic metrics are used to measure the real economy.