Ever since Osiris expansion came out and I managed to finish the game I haven't touched destiny 2 up until a week ago when I bought both shadows keep and forsaken, naturally during the time I was playing Destiny 2 was accessed through the blizzard app and now its on steam. After I downloaded and changed the account to steam with cross save it took a whole to catch on to the changes. And I was able to access the collection and I have access to my exotics however all the catalysts and skins I had owned previously aren't found anywhere.
If you go triumphs>account>exotic catalysts, you’ll be able to see all your catalysts that you’ve unlocked. As for the ornaments, if they are already unlocked they will be in a drop down menu called ‘Appearances’ when inspecting the weapon or armor piece.