Is there a way to transfer my Destiny 2 profile from "BTL Net" to this account?
The attached video shows I already have purchased Destiny 2 and the "Curse of Osiris" DLC, and I don't want to buy a second time if I can help it.
If a profile transfer is not possible, I ask that you please add the previously listed to my Steam profile.
As others have said, you missed the deadline to transfer your characters, so you will have to start fresh.
As far as your purchases go, Destiny 2 was made free, and the Curse of Osiris and Warmind DLCs were incorporated into the base Destiny 2 game.
While the Curse of Osiris campaign is now in the Destiny Content Vault, the exotics associated with it (and Warmind) are now part of the general loot pool; those DLC licenses are not required to access what content remains within the game.
The purchases you previously had are no longer necessary to access the content available that was part of them, so you are not required to buy Destiny 2 or Curse of Osiris on Steam.