A lot of people are currently switching over from WhatsApp to Signal right now, and the two are comparable enough that Signal can pretty much act as a drop-in replacement for WhatsApp. They have very comparable features, and Signal is easy enough to use that it's adoptable by non-techy people.
Does something similar exist for Facebook? I'm fully aware of the network effects that keep people on Facebook, but let's pretend a lot of people wanted to leave that platform and migrate elsewhere. Is there anything that has a similar featureset and that is usable by the general population?