I am not a UI designer. I am no expert here.
Like many of us, my initial reaction is to criticize because it feels like they asked ChatGPT to create the script for this demo video with a lot of filler words. It's exhausting parsing all the "connecting to the physical world" phrases just to understand they added refraction between UI elements. I wish someone would just speak these new things to me straightly.
However, I can't pass over that Apple's Design team is top-notch. They absolutely take the little polishes to the highest degree they can. A lot of it doesn't look necessary. We clown on Apple but comparing the iPhone UI to Android, there are just many less visual glitches and jagged edges on iPhone. Apple is known for its polish. A lot of it looks like repeating the visual eye candy of the past that people quickly grew tired of.
To me this looks like they're bridging the gap to running the UI as a full 3-dimensional physics sandbox. They talk about how the new glass surfaces are broken into 4 layers that adapt to each other. I think this is cool how this works mechanically, but I know this will be hardly be legible to most users. I'll have to train myself to get used to it. I do prefer flatter, more minimal designs with less complexity.
I think the future is the UI going from 2d elements to 3d elements. I think scrollbars and buttons and such will be defined as full material objects in 3d space in the future with inherent weight and inertia, etc. I know as an outsider I'm probably naive that this is already so in some ways. Right now most UI elements are 2d materials emulating 3d ones. I do think we've moved up to the point where our less powerful devices like watches and phones can handle running a 3d physics sandbox all the time, and sipping power while they do.
This is the precursor to 3-dimentional physics-based UIs. It's sort of a joke but I do expect ray-traced shadows in the future/soon. Much less static assets, many more materials. MMW~