Rumour: Your PS4 Saves May Not Work on All Upgraded PS5 Games

Really this is just a different approach with the PS5 Upgrade Program and XB Smart Delivery.

In PS5 upgrade you get to play the best version of your game for both PS4 and PS5 but game saves and trophies are allowed to be different.

For XB Smart Delivery you have to carry the game saves and achievements to both XBO and XB Series devices.

Just a difference in how the two upgrade/cross buy programs operate. There are advantages and disadvantages to both approaches.