I'd point out that for most people (I suppose that could change, and I wouldn't be upset if such changes resulted in better privacy), messaging is often phone-based and includes folks who use secure methods like Signal and Matrix as well as those who use iMessage and OEM SMS clients.

When it comes to that sort of messaging ("I'm running a few minutes late and will meet you inside the restaurant," or similar) I don't (and won't) separate those out. I just use Signal for all such messages.

Which makes for inconvenience when (especially iPhone users) install Signal and still use iMessage.

I'd add that if I have something to discuss that I don't want recorded (don't forget that it's not just your device that puts you at risk, anyone who's received such messages do so as well), I'll use encrypted voice calls (with the assumption -- valid or not -- that the other participant(s) aren't recording that conversation) with Signal or Matrix.

In both my personal and professional life, I've always made sure to only put in writing that which I wouldn't care if it was shared with the world.

Which is no different than it's ever been. I'm not sure why anyone thinks this is a new thing or that somehow "technology" obviates the need for good OpSec. It never did and still doesn't.

Matrix bridges support iMessage and SMS and even Signal so you do not need to fragment your communications to multiple apps if you do not want to.