If you have Destiny 2 on PC right now, you have it on Battle.net: in which case you may want to listen up.
I'm sure you've heard, but Bungie is in the process of stripping the game from Battle.net and moving it to Steam. They announced this several weeks ago, but starting today, you can actually begin the migration process. Just go to this URL, click "get started," log in, and follow the prompts: I tried it this morning and it takes around 30 seconds.
If it worked, you'll see the following message: "You are now ready to play Destiny on Steam for Shadowkeep launch. Review your future Steam account below." Note that this is a "one-time, non-reversible" transfer. You can do the same for cross-save once the process is live. As a reminder there are some provisos for cross-save (silver doesn't transfer, you need to re-buy games, and if you disable it, you need to wait 90 days to re-enable it).
Do all of this early to ensure that the shebang goes off without a hitch, and you can contact Bungie support before the October 1 release date of Shadowkeep, when the Steam edition is live.
PC Move [Bungie.net]