E2EE doesn't mean anything if you have the same entity controlling the server as is controlling the endpoints.
If you control both ends of an E2EE communication and they are closed then you gain nothing over normal TLS encryption, you still trust the authority. (Whatsapp is obviously closed and yes, signal can be considered effectively closed as their client is not reliably or reproducably built from public sources and has hidden their agendas before[0]; and even depends on binary blobs from Google..)
I know your favourite closed/walled messenger platform is basically religion at this point: but for heavens sake; please understand that unless you're auditing your clients or you can run trustable third-party clients; then end-to-end doesn't mean anything at all.
It's just marketing buzzwords.