Other threads on this topic lead me to suspect that it will come up once your car is built. I just get "discover current phase" on the "vehicle" page, but no "details" button and no manual.
Here's a thought: make sure the dealer for your '24 used the same Porsche ID as they did for your previous car. I had to log out from the app and log in again with a different email address as the username in order to see the build status of my '24. I suppose if I log back in with the old one my now-sold '21 and its owners manual will reappear.
Here's a pet peeve: Car manufacturers seem to deliberately print only one owners manual for every trim/package level, as if to rub your nose in it ("Optional equipment shown" translates as, "You may not have this feature, see what you're missing?"). That makes it frustrating to find the instructions that actually apply (as an example the overhead switches for the interior lights on a Subaru might not look anything like what's shown on the sketch in the manual, or on my wife's Audi when it says, "On cars equipped with.." I'm thinking, "Do we have that?").
So, now if there's an app with my vehicle and VIN number, and the owners manual is now digital, why can't they customize it for my optional equipment??? That would be a justification for not letting everyone get the digital manual in the app...