It does not matter whether you encrypt illegal content, things do not magically turn legal once they are encrypted.
I wasn't suggesting it was, I was just pointing out that it wouldn't be easily provable that you were in possession of such content.
Plaintext cannot be set up to be E2EE, that is a contradiction in itself. Rooms can be either unencrypted or encrypted. If they are, messages are encrypted.
I feel this is a bit pedantic as I would assume that you understood that I meant text messages, unless you are saying that all forms of messages, including media like images and videos, are encrypted in e2ee rooms, in which case that is information I did not have.