Greetings!

I downloaded Oxenfree yesterday and have completed it, I then "Continue the timeline?" and completed that too. But I didn't see any of the new stuff the DLC video is showing, tho the second playthrough were different, it didn't have any of that in it.

Did I do something wrong or something I have missed? Some dialogues I need to select or something?

There are many possible endings (at least 7 maybe more), "The new stuff" is two years old and definitely in the game.

I should have checked the date that's for sure. But still not seeing the "new" stuff.

I am aware of the many endings, but so far I can see in the guides they don't seem to differ in terms of the actual gameplay (ending is different tho) just some dialouge changes etc. Would you be willing to say at least one "route" that will let me see just a bit of the "new" stuff? PM or spoiler tag etc.

As far as I know there's no DLC available or even planned, so about what video are you talking about? (If it's in game I haven't completed New Game+ (Continue the timeline?) yet, so I can't help then)
But all the update changes should be downloaded automatically.

It came out 2 years ago, I forgot to look at the date.