“What’s your solution then?” Is one of those lazy rhetorical tricks to discredit any criticism of a complex problem.
Like, no, I will not come up with an easy solution to capitalism over a couple of social media posts. But expecting that any anti-capitalist must have a ready-to-use solution to everything they criticize is just a convenient method to shut down that criticism and cement capitalism and “inevitable” or even “natural”, to make even the idea of a different system seem impossible and not worth thinking about.