Conversations on Android and Siskin on iOS.
One non-techie parent has Siskin running on their iPhone and it hasn’t skipped a beat in years of messaging using omemo-encrypted XMPP. For servers, they’re on tigase.im and I’m on conversations.im.
Here’s a guide on optimum siskin settings; I don’t know if defaults are better now or not.
Conversations.im is free on fdroid but it’s well worth paying something to the developer directly.
As long as there’s no cream in it, we’re good.