https://www.gamespot.com/articles/destiny-2-pc-preload-now-available-heres-how-to-do/1100-6454178/

Ahead of Destiny 2's release for PC next week, you can now start pre-loading the shooter. As announced previously, pre-loading started on October 18.

Destiny 2's PC version is available only on Blizzard's Battle.net platform, not Steam or other digital stores. You can buy the game right here and start pre-loading right away. Of course, Destiny 2's servers don't go live until 10 AM PT on October 24, but pre-loading ensures that you can start playing right away come launch.