The messages are signed by cryptographic keys on the users phones that never leave the device. They are not decryptable in any way by google or anyone else. Thats the very nature of E2EE.

How end-to-end encryption works

When you use the Google Messages app to send end-to-end encrypted messages, all chats, including their text and any files or media, are encrypted as the data travels between devices. Encryption converts data into scrambled text. The unreadable text can only be decoded with a secret key.

The secret key is a number that’s:

Created on your device and the device you message. It exists only on these two devices.

Not shared with Google, anyone else, or other devices.

Generated again for each message.

Deleted from the sender's device when the encrypted message is created, and deleted from the receiver's device when the message is decrypted.

Neither Google or other third parties can read end-to-end encrypted messages because they don’t have the key.

They cant fuck with it, at all, by design. That's the whole point. Even if they created "archived" messages to datamine, all they would have is the noise.