https://www.pcgamer.com/destiny-2-forsaken-players-find-easy-new-way-to-loot-chest-in-the-last-wish-raid/

Nearly a week before the release of Last Wish, Destiny 2: Forsaken's new raid, players not only found a way into the raid area and up to a raid chest, they also happened upon a sketchy method to repeatedly loot the chest, with some players obtaining full raid gear sets before Last Wish was even released. Now that the raid is actually out, players have focused their secret-hunting efforts on the mysterious Wall of Wishes found at the start of the raid, and after a little tinkering they've uncovered an easy, legitimate way to loot a raid chest. It doesn't reward powerful gear, but it is a fun and fast way to nab some Last Wish weapons and armor.  

Per the above video from Ninja Pups, all you need to do is enter the correct Wall of Wishes code and then navigate a few jumps. To reach the Wall of Wishes, enter the raid as normal and make your way through the crystal cave at the start. But instead of turning right into the lair of Kalli, the Corrupted, continue straight and look for some mossy platforms. The first once can't be seen until you jump out a bit, but it's there. Follow these platforms up until you find the Wall of Wishes.