They make the app that stores the plaintext at each end... they don't need to decrypt your messages across the wire to read them.

Ah I understand now, thank you. So they can actually read it just not in transit but from the app, isn't that a security violation?

All e2e encrypted apps can do this. It's the price you pay for a completely closed ecosystem that coddles you at every turn because you're too much of a little bean to know what real security is.

Edit: this isn't a dig at you, it's a dig at how google and apple treat you

I didn't know that they are able to do this, now that I know it just makes perfect sense.

A what violation?

I kid. But only sorta.

They advertise e2e as something that is to secure your messages and no one can read it including them, just got surprised when I realized they can view all the messages before transit, I never even thought that that they can do that before encryption

They control the software doing the encryption & decryption - they could ship your private keys to themselves if they truly wanted to be evil.

Who would know?