I found the easiest way to get platinum trophy.
This works for Digital or Patched versions. I'm prety sure it will work on unpatched as well.
You have to do it on 2 runs, because you have to choose Wyatt or Fergus.
Finish the game on "Can I Play, Daddy?" difficulty, following the walkthroughs to get all collectible (Gold Items, Enigma Codes, Letters);
On the first run, choose Wyatt or Fergus timeline;
Solve the enigma codes;
Start a new game on Extra Mode > 999 (it is Über by default, see enigma description);
On this second run, choose the other timeline;
Finish the game as fast as you can;
After that, keep the game running on Extra Mode menu for about 1 minute (I had to wait that to get trophy).
Enjoy one more Platinum on your profile