What? Why can't iOS just prevent apps from automatically reading the clipboard without the user's private consent? It seems useless to encrypt the data when you can just deny its transmission. I'm jailbroken right now so I just installed NoClipboardForYou[1], I'm sure Apple could make something themselves to fulfill the same need.
[1]: https://www.reddit.com/r/jailbreak/comments/hlabn3/free_rele... (Normally I'd link directly to the GitHub repository but this Reddit thread has more info).