PS4 Saves May NOT WORK on All Upgraded PS5 Games?!

There is a bit of confusion in regards to wether your PS4 save will carry across to the PS5 if you utilize the title's free next-gen upgrade with titles such as Spider-Man: Miles Morales, Maneater and others. This seems to suggest that cross-save has not been mandated by Sony and so some developers may opt not to support the feature.