Any word on new dynamic backgrounds?

At this time, dynamic backgrounds are only available on the Series S/X and can't be customized. If the video you saw was done on a One, then the person doing it is doing something that violates the terms of service.

If you are on a Series S/X, when you go to settings and change your background, there's a section for dynamic backgrounds.

i want dynamic background themes

I like the achievement backgrounds. It would be awesome if they added dynamic backgrounds to the Series X, just like the PS4.

No. It's a dynamic background which is only available on the Series S/X

Just look online for a 1920x1080 image (or make one yourself) and then go into the xbox, view the picture, set as background. Sure it's not dynamic nor will it give little background items to your friends (is that even on the new dashboard?) but it's great
for customizing without spending MS points.