I once heard my spouse complaining about Signal, and how they only had it loaded on their iPhone so they could talk to me. I asked why Signal was not their default SMS application, like it is on my Android phone. And that's when I discovered that Apple hoards certain core phone features for itself.

Signal for iOS cannot send or receive ordinary SMS messages. This is a significant impediment to adoption of end-to-end encryption, because checking two applications to receive different kinds of messages is inconvenient, and inconvenience is the death of mobile applications.

And here I note that Apple is effectively punishing users for apostasy. If you leave the Apple ecosystem, you are excommunicated from your former chat contacts. I, having never entered the Apple ecosystem, have no problem being included in group chats with iPhone users. (I occasionally have problems receiving media attachments, though.)

This makes me even more wary of ever buying in, knowing that trying to leave later will cause all manner of problems as I try to reclaim functions that Apple will take over. Entering the walled gardens make me afraid of being locked in.