There’s a few trends at play:

Young people in Europe and North America do not use Facebook anymore, if they even have an account at all.

It is still popular among older users in North America. This is one of the wealthiest demographics on earth, so Facebook’s advertising model will be ok for the foreseeable future.

Growth is still positive on Instagram and WhatsApp, though Instagram’s engagement levels have begun to decline.

Facebook’s main growth areas for all three apps are in the developing world. They pay carriers to allow Facebook to be accessed without counting against user data limits, so in a lot of these countries Facebook is synonymous with The Internet. Young people in these countries still see Facebook as cool, and they aren’t as likely to seek out platforms to avoid their parents on. The key problem is that these markets are not worth very much to advertisers because they have low levels of discretionary spending. This makes operating in these markets a long play for Meta; they spend some money on subsidies to build a user base in the hope that the users will gain higher levels of discretionary spending in the future, increasing the value of the market for advertisers.