That's why I skip the Signal intermediate stage plain and simple: once Signal inevitably enshittifies (a property of centralised services), the people you painfully brought there will no longer kindly listen to you when, lesson learned, you will try to pull them into federated services.

For anyone else (i.e. the majority, which already has 2-5-10 messaging services on their device depending on how you count), quicksy.im does a decent job at emulating the onboarding experience of phone-based social graphs (WhatsApp & al.) and substantially lowers the barrier to being reachable over XMPP.