As it turns out, the appearance of Destiny 2's damage numbers has been a bit too over the top, the dev claims, which is why they'll be tweaking them, removing last digits and whatnot. Note that this is a UI update, as the actual damage remains unchanged.
As for game-related changes, Destiny 2: Shadowkeep will bring newly tuned PvE difficulty, ensuring that combatants from 10-40 level take less time to kill and inflict less damage. Higher-level ones continue to increase in difficulty, becoming immune to damage once they hit 100 Power levels above players.
PvE difficulty changes will be reflected on higher-level combatant nameplates and Bungie hoping it will "widen the sweet spot where fighting higher-level combatants provides a fun, challenging, and rewarding combat experience for a more enjoyable Power climb. Also, allow players looking for even greater challenges to confront higher-level enemies."
Destiny 2 players' experience no longer dictates character levels and all their characters are now level 50. will instead be used for the Season Pass, while experience rewards are tweaked to better fit the Season Pass and Seasonal Artifact progressions. All the existing gear now has a minimum of 750, which applies to new characters as well.
Bungie set the soft cap to 900, and all the drops up to that point will be higher than whatever you've got. In practice, just play and you'll be rewarded. Once you're past 900, however, you'll have to rely on powerful and pinnacle rewards to boost Power.
Some eagle-eyed players noticed that the launch trailer for Destiny 2: Shadowkeep features Trials of the Nine armour, but this was apparently Bungie's mistake and there will be no Trials of the Nine in Season of the Undying.
You can find the full patch notes here