as far as I know (correct me if I am wrong)

nostrdms + vpn:

who writes who and how much = known to everyone pseudonymously,

what is writen= unknown

simplex:

who writes who and how much= unknown,

what is writen= unknown

whatsapp, twitter, email:

all = known to elon, zuck, bill etc and their superiors

signal:

who writes who and how much = known to signal + gov,

what is writen= unknown

element/matrix+vpn:

who writes who and how much = known to serverhosts (+ gov) pseudonymously,

what is writen= unknown