The other end of the conversation escrows the key on any messenger. Otherwise how would you read the message? Unless you consider Snapchat, but that's not End to End Encrypted.

And are you really sure that Signal or your preferred messengers don't also have Zero-Click exploits? After all, they aren't sandboxed to the degree iMessage is with BlastDoor.

There is no such thing as a "truly-secure option." As anyone truly concerned about security will tell you.

You will be forced to make compromises somewhere unless you want to live under a rock in the desert. You can't drive without a State ID, can't get a home loan without credit, can't work without a Social Security Number except under limited circumstances, can't make money without reporting to the IRS, and so on. It's entirely about what compromises you want to make, and the tradeoffs therein.