I always laugh when I hear about meta's end to end encryption because it isn't remotely true in the sense that people would care about from a privacy standpoint. I know it is the case for messenger, I have not confirmed for other meta services, but in messenger the messages are encrypted in the way you would expect with the one big caveat being that meta stores your private keys on their servers. Iiirc meta explained that it is still e2e because they don't unencrypt it which I find hilarious.