Reactive UIs are so horrible. It sounds great, in theory, and I believe there might be a way to do them well. They do address the infinitely nested submenu problem. But - especially on mobile, as you say - having UI controls change is fraught.

On the desktop, it’s horrible when I user has to constantly search for functions because the buttons and menus are constantly changing with small context changes. I’ve observed even power users hunting for an operation because the button bar is constantly re-arranging itself. I’ll never forgive MS for introducing that awful feature.

And on mobile, it’s worse, because widgets change as you’re using it and you lose control of the process, or UI elements disappear or move as you’re trying to click on them.

UI designers are trying to address the complexity paradox: either you constrain user options, or it’s impossible to prevent many functions from being hidden in nested option trees - whether pages or menus - where users struggle to find them.

I think the “search” function is the best solution; assistants are, in most cases, the worst.

My current pet peeve is the trend in launchers to change the pinned app bar contents on Android with commonly used apps, so that you’re never quite certain which set of apps are going to appear, and in which order. I always turn that off and pin the apps I want: stop re-arranging my shit!