On Android, it asks you when you set your passcode for the first time.
Super fragmented, but Nexus 5X had it.
My Sony Xperia also asked me at lock screen configuration. I could choose either way, but could not ignore the question.
Galaxy S7 asks you too. I remember now that you said it.
Agreed. It's usually buried in the device settings and also in Messenger and Hangouts. Signal gives you a few different options as well. But it should be more visible to all users, not just those of us that dig through settings.