A business is valued as roughly profits times growth. The issue here is Meta used to have both growth and profit and now it mostly has profits. It doesn't mean the business is doomed obviously, but it means it should trade at a much lower valuation. A correction in PE means a huge drop in stock price despite profits still being there.

Google is growing its top line over 20% YoY and has a PE of 20. What PE would you give another business that sell ads but has a stagnating top line? Probably much less than 20.