can Destiny 2 - Annual Pass bought for two users?

Destiny 2 DLC is not shareable. Both users will need to buy it seperatly

You're close. Your girlfriend adds her account to your console and sets it as her account's Home Xbox. This is because it is against the Xbox Live Code of Conduct to sign into accounts you do not own. After she buys the content, she can then add it to
your console (or she can set the Home Xbox to auto-download content). Then, you sign in as yourself and you'll be able to access content she owns.

Hi there,

Essentially if you guys share one console, both of your accounts should already be set up so that the console you share is the Home console for each account. It's the default action when you add a new account to an Xbox. However, you can check in your settings
and make sure. From Settings>Personalization>My home Xbox and it will tell you whether to make that your home console or to remove it if it's already set. Don't remove it if that's what it says.

https://support.xbox.com/games/game-setup/my-home-xbox

One thing to note is that not all DLC content for games is sharable as it is restricted by the developers or publishers of the game. Unfortunately this does apply to Destiny 2 DLC and I don't believe that content is sharable between accounts. The game I
think is but not the DLC from what I have seen before. I suggest at least setting up the Home console setting and possibly the DLC will be playable on the other account.

So if i got thos right - the xbox home feature is new to me - i change to her account - activate the home feature and install the annual pass - then i should get it also via my account?

DLC that opens up additional content (more story levels, more maps, etc.) should be available to all users via the Home Xbox feature. Special content (like bonus weapons, bonus XP upgrades) is usually limited to the account that purchased it.