We should see an improvement in game quality for the platform once last-gen sales drop off enough that developers only need to target current-gen.
Right now any game that comes out for both PS4+5 is bottlenecked by PS4 memory and performance, with only easy wins taken for PS5 like higher quality assets and faster IO/FPS.
Designing a game for current-gen platforms from the ground up is when we'll start to see some more impressive features, but there's still money on the table for PS4 so it'll be a few years (IMHO) before we see PS5 exclusives as the norm.
WhatsApp is closed source, and obviously it must be able to decrypt messages for the end user to read them. Anything could happen to the unencrypted data at this point. Therefore it's less secure allowing conversations to flow into that app.