Fortnite makes money by selling digital in-game goods. Their revenues could grow infinitely without their material footprint expanding one iota. What they demonstrate is not infinite growth, but the capacity for infinite growth in a finite universe.
Value, at the end of the day, is subjective. Growth is a measure on this subjective value. It is not a measure on material inputs.
The proposed metric, a product of population and incomes, is unbounded (in aggregate). Population isn’t. But nominal incomes, a function of the unbounded money supply, is. Real incomes are trickier, but they--too--are unbounded. It just requires some fraction of the basket be immaterial. As long as that component grows sufficiently, the real value of the basket–which, again, is subjective–grows.
This isn't some edge-case philosophy, but a well-recognized effect of the subjective nature of value. (The physicist in me points out that the observable universe has, based on known physics, a finite computational capacity, but that objection merely illustrates the absurdity of proposing a practical upper bound on growth.)
We're used to thinking of production as making cars and ships. Those activities represent a falling share of human activity (weighted by value). To illustrate, witness the falling material intensity and energy intensity of GDP growth.
Anyway, let me rephrase your argument to make sure I understand it correctly:
There exists resource sinks like Fortnite, media & alike. Thus regardless of how much growth we will have / more efficient we become, even more would be better so we can spend it on those sinks.
This seems technically correct, but I doubt this is how our civilization should spend the finite amount of resources available.
Infinite growth and finite material resources are perfectly compatible. Case in point: Fortnite.