AirBnB's redesign isn't a indicator of design trends changing. Most of the app remains minimal and "flat", the dimensional flares are mixed inconsistently throughout. The app could more easily flop back to fully minimalist than it could into a fully 3d design language.
Also dimensional icons have existed within flat UIs as app icons for quite some time, though some platforms have had periods of both flat icons and UI. In a sense they are adopting them in this existing usage as sub-app icons.
The oddest thing is the glossy "new" tags, they are the only tags within the UI which are glossy. Having them mixed with flat tags and flat buttons is honestly confusing, they look more like buttons than the actual buttons do.
> Back in the early 2000s, UI design like this had a high skill ceiling. It took years to master lighting, materials, and depth. Now? That level of craft is often just a prompt away.
Mastering any design style takes time, and the skill ceiling is not meaningfully different if there even is one. I'm also highly sceptical that AI would be able to be consistent enough whether generating flat or 3d icons.
Yeah, the icon style is the part I care about the least when taking about flat design. It is the fact that it removes all visual affordances that something is interactive. Clickable items that don't look like buttons or hypertext, they just look like the rest of the page. Scrollable regions that don't have scrollbars or any other visual clue that there is more content below or to the right, unless some of that content happens to be cut off by the invisible region boundary. Windows whose only indication of which is selected is the title goes from dark gray on light gray, to medium gray on light gray.