Yet I just found an article that said that MAU was 3.065 in 2023 and 2024 and 3.07 in 2025 (i.e. MAU is flat not decreasing). Did you drop a zero?
AFAIK there is no consensus that Facebook usage is declining - however that narritive gets told by people. Of course, it might depend on which country you look at.
You made that up, or you checked stats?
A quick Google says that Facebook is still growing at about 5% and that Meta revenue is up a lot.