In addition to SonicFusion2K's statement, you cannot buy Forsaken or Shadowkeep DLC from the Eververse store. Purchasing Silver wasn't necessary to begin with. The DLCs are listed in Eververse purely to enable you to see what DLCs the game has detected you having full access to (marked with a checkmark). To purchase Forsaken on PC, you need to buy it on Steam. You can do so here: https://store.steampowered.com/app/1090150 .
Well this is great, isn't this great