The article is specifically not referring to information that's sent to Apple servers - it's about information on the phone only, accessible through forensics tools with physical device access.
Signal's server-side push notifications only contain a "wakeup" message. The actual message popup is displayed after decrypting the message contents locally on the device. Of the things you mentioned, only the time of notification is visible to Apple/Google.
Signal's server-side push notifications only contain a "wakeup" message. The actual message popup is displayed after decrypting the message contents locally on the device. Of the things you mentioned, only the time of notification is visible to Apple/Google.