It's weird to hang up on this specific item because they do actually offer an E2EE icloud option. Lose your key: lose your data.

https://support.apple.com/en-us/108756

Nobody has it on, and unless BOTH sides are using it, your iMessage conversations are all readable by Apple, because they are backed up twice - one for each end.

This option is also disabled in the UK - an intentionally preserved backdoor for government access.

https://support.apple.com/en-gb/122234