One of the fundamental differences between iOS and Android is that on Android you can replace most preinstalled apps with a third-party app for the same purpose

One of the fundamental differences between iOS and Android is that on Android you can replace most preinstalled apps with a third-party app for the same purpose. You can use third-party camera apps, keyboards(iOS too for some time), messaging(SMS) apps, web browser engines, ... Signal requests the status as default messaging app, which imho is a problem when combined with inexperienced users who tend to just click "OK" to get rid of popups and error messages, and now don't understand why they can't send a picture to someone in their contact list. And yes, Signal just lists everything in the same interface. For non-technical users this can lead to a lot of unexpected behaviour.