1. How narrow is your screen? The FAB is typically used over scrollable full-width list items.
2. Using a design system does not release the app author from their UX duties, like making sure the UI works as best as possible.
Even Mobile Safari messes this up on occasion — sometimes the URL bar at the bottom obscures the bottom of a page, and, while one can temporarily reveal it by dragging up, the content rubber-bands right back down when the user lets go.
But I think this misses the point. Mobile Safari has a heuristically auto-hiding “toolbar”, and the heuristic is far from perfect, and the toolbar overlays the content, and Safari tries to offer some features that maybe let webpages move their content out of the way when hidden. And the result works poorly sometimes.
Fundamentally, doing a good job of having a control sitting on the section of the screen that shows content and mitigating the risk that the control obscures the content is hard.
No, it’s not, because it floats over the actual content, which means that the user can neither see nor interact with the content under it. Of course, no one carefully designs the rest of the UI to make sure that content doesn’t get stuck under the floating button.