Check your Steam library. It should list all DLC you have on Steam. If it says you have Forsaken, see if you can download it. If you’ve played through Forsaken on Xbox, and you don’t own it on Steam, I don’t see any reason to buy it for PC unless you plan on doing Last Wish raid or re-playing the story missions or Shattered Throne. Dreaming City and Tangled shore patrol zones and lost sectors are now included as part of the FTP new light so you’ll have those either way.