With Signal's default settings, Google reads your Signal messages when they come in through push notifications.
Correct me if I'm wrong.
Edit: For those in doubt, last year, I started seeing content-aware auto-reply options in my Signal message notifications; that is not a function of Signal, but a function of Google's Android. One could escape it by using a de-Googled Android like Lineage or Graphene, or by hiding the message content (which is not the Signal default) and would surely hurt Signal's adoption, when you have to unlock the app to read each message.
that's not how push works. usually, google would only know you received a notification, but not it's contents. that "dummy" notification wakes the app up, which decrypts and shows the real notification.
content aware stuff runs entirely locally on your phone, so no data is sent to google (unless you have telemetry enabled, in which case the reply or action you used will be sent to google together with the next telemetry data upload)
yes, some apps actually push the content directly through the push system, but that's not how this is handled in most apps that handle private data in notifications.