Depends on the context and who I'm talking to. That one makes a bit more sense because it is renaming the overarching company to separate itself from one of their products that is declining in popularity in some circle. It isn't unusual that people outside tech forget WhatsApp, Facebook and Instagram are all the same company.
Facebook. I'm _kind_ of surprised they haven't changed it back yet, tbh; it is quite weird that the company is named after a failed product.
Brand name changes actually quite rarely take, in the long term. No point being over-eager to adopt them.
Do I call what Facebook or Meta? You are talking about two separate things.
Facebook. But Meta is slowly creeping in. Renaming a popular term takes years or decades.