If you’re still using Battle.net to play Destiny 2, you’re gonna need to change that soon. On December 1, the game’s service will be completely removed from Blizzard’s service, making the PC version only available via Steam. This change also means that players will no longer be able to use the Destiny Companion app via Blizzard — or create Bungie profiles.
Of course, the transfer isn’t as simple as just connecting your Bungie account to Steam — although there are directions for that available on Bungie’s site. You’ll also need to make sure that anything directely related to the Battle.net service, such as redeeming codes, be done before you make the transfer. If you have both Steam and Battle.net versions of the game already, you’re also going to have to decide if that transfer is really worth it, because the Battle.net version will replace the existing Steam version. (No merging here.)