Hi there. If you switch to PC, the only things you would need to purchase is Shadowkeep and Forsaken. Everything else will be available to you for free.
I asked this question last week. So if you buy Shadowkeep on PC, you get Shadowkeep and whatever else is available with New Light. So you get all patrol areas, all strikes, crucible and gambit. It will also feature The. Leviathan raid, and the new black garden raid. So basically you’re not getting the forsaken story content or raid. You don’t get forsaken, and I don’t think you get the year 1 DLC because when I liked my steam account, steam said I didn’t have it.