Google‘s or Apple‘s push notification servers turns out that doesn’t matter so much from what I undertstood.
Can you elaborate? It’s my understanding that push notifications are only used to trigger Signal to check if there are messages - the message data and who/what triggered it is not being sent to Google/Apple. If you don’t trust push notifications, you can always use a De-google’d phone and the Signal APK which will fallback to polling the server; this will obviously impact battery life as the app needs to constantly be checking for new messages.
It Takes Two is such a fun game to play with a friend. Highly recommended.