I don’t know what may have changed as I am an iPhone user, but about 10 years ago I worked in a small security role for a fairly large company, and the communications company we were using was more than happy to hand over sms logs as plain text. I would personally never send messages to anyone I was sure wasn’t encrypted and I can tell that by the blue bubble. I just don’t know when it is green.

I don’t know what has changed as I don’t keep up with it, but I am still dubious about messaging outside the Apple ecosystem, which is ok for me as I live in a country where most people use iOS