According to Apple, you can have iCloud backup enabled while maintaining E2E encryption with their Advanced Data Protection option:
https://support.apple.com/en-us/102651#advanced
You do have to be sure to not enable web access via icloud.com
You also have to make sure everyone you contact did this, which is impossible.
Much easier to use a 3rd party app like Signal.
You also have to make sure everyone you contact did this, which is impossible.
Much easier to use a 3rd party app like Signal.