They make a copies of that plaintext database for backup purposes:
One on google drive (not mandatory, but it IIRC by default), which is still plaintext but not accessible to yourself.
One on your local SD card (if you ask for it), which is encrypted with a key that's on your phone but was sent down from FB servers. If you switch your phone, and try to restore that database, it will contact FB servers to retrieve the key.
> if that's the case then facebook can't "give you" the key, because they don't have it, it's supposed to be on your phone and only there..
Regardless of the backup encryption, e2e doesn't mean that they don't have the key; it just means that it leaves one phone encrypted and enters the other encrypted without being decrypted along the way -- unlike, e.g. regular email, which is usually encrypted in transit by TLS, but gets decrypted and re-encrypted at every stop along the way.
if that's the case then facebook can't "give you" the key, because they don't have it, it's supposed to be on your phone and only there..
Is there something i'm missing here ?