The Shadowkeep DLC for Destiny 2 is currently on 40% off at Steam. This makes it the current historical low. The base game is also free to play on Steam, so you can try it out before deciding to jump into more content with the DLC.
The digital deluxe edition is also 25% off. It includes Shadowkeep, Season of the Undying and Shadowkeep Deluxe Pack.
Was there ever any clarity on how expansions work with cross play?