Does anyone know if the 4k ui update for the series x applies for the series s aswell?

Yes but as mentioned you will have issues

It upscales not native

Only the xbox one x and series x are 4k native

https://www.tomsguide.com/face-off/xbox-series-x-vs-xbox-series-s

The reason why smart delivery compresses files because of the CPU and GPU power and storage limitations

https://www.xbox.com/en-CA/consoles/compare

True 4k vs 1440p

Most.games will.only run 1080p max on series s

It will do less CPU intensive stuff like 4k streaming

Series x does 4k 60hx with possible 120hz (dropped fps )

Xbox one x does only 4k 30hz

The Series X is physically larger than the Series S and has a disc drive where the Series S does not. The X will be more powerful and run games in true 4K.

This article has a pretty good side by side comparison of the specs. https://www.pcmag.com/news/xbox-series-x-vs-xbox-series-s-whats-the-difference

What resolution are you trying to run at

If 4k 120 Hz then no it won't run at thaf

The max for series s is 1440p at 120hz

It will play at 4k bur only some games and with issues

The series s is meant for 1080p 120 max

With suggested 90hz

The xbox series x and ps5 and switch pro are the only 4k consoles

One x does 4k at 30hz and ps4 pro upscales

Does the 1080p support go for both the Series S and Series X, or just the Series S?

1080p is supported by both Series X / S,

However if your only playing at 1080p and have no plan's of upgrading to a 4K TV / Monitor, The Xbox Series S would be recommended as is a 1080p / 1440p gaming console and you would save £/$200, than getting the Series X, as that is a 4K gaming console and
you would never get to use the full potential of it if used on a 1080p TV / Monitor.

https://youtu.be/VIHny-XP8jM

So, we finally got to see the next gen "little brother" Series S. It's kept to a design not far from our current One S, and i my opinion looks pretty good. Properly not one that i am going to pick up. I will definitely go Series X all the way.
But a nice cost efficient alternative and a great entry model for new xbox players.

What are peoples thoughts ? and are you thinking about picking it up ?

The way i see it, i don't see the Series S as an entry model, it depends on what the resolution of TV / Monitor is being used, because the Xbox Series X is more aimed at 4K gaming and the Xbox Series S is more aimed at 1080p / 1440p gaming,

For someone who does not have / own or does not plan to upgrade to a 4K TV / Monitor, then the Series S is perfect choice to get and will save you money by not paying for something that you'll never get to see or use the full potential of the Series X,

It make no sense to me why anyone would buy a Series X just to play at 1080p, but there will be people out there who will do just that, to me, that's just wasted money in my opinion,

My thoughts are...

If your gaming at 4K, go with the Xbox Series X,

If your gaming at 1080p / 1440p, go with the Xbox Series S,

I have a 4K TV and a 4K Gaming Monitor so for me, I'm getting the Xbox Series X.