And while it will always be controversial, I'll say it over and over again: you MUST support some kind of adversarial interoperability for a messaging client, at least if you want me on your service. In the US, that means having some degree of SMS support since that's what most people can use by default. In many parts of the world (at least pending the new EU directive), you don't even have that since the primary means of messaging most people is proprietary services.
Signal walked back from even bare-bones SMS support in their app. If they had supported it, including forwarding messages to desktop/tablet clients , I am sure it could've given them a high degree of user retention. Maybe even some opportunities to conversion, e.g.,, a user getting a prompt when starting a new SMS that the sender is on Signal. They instead focused on maintaining the walled garden and that creates an INTENSELY high up-front cost. For someone like me, who puts a high priority on juggling as few of these apps as possible to communicate with people, it's an unreasonably high one. I have no more desire to try and fight to convert all my parents to Signal as getting them onto a Discord server or any other random, narrow-field service that they will not be able to ding strangers on.
It's absolutely unintelligible to me that no competitor has seen plainly what makes iMessage so strong: that it works by default with pretty much everyone with nearly zero friction to the user by supporting a nearly universal fallback.
It also is why it makes so much damn sense to me that the EU passed the adversarial interoperability rule. Because the had very close to nothing for a universal fallback.