I can't speak about Material Shell, but on dedicated tiling WMs, you get to select a subset of apps that you want to always open in floating mode to accommodate

I can't speak about Material Shell, but on dedicated tiling WMs, you get to select a subset of apps that you want to always open in floating mode to accommodate the use case you are describing. Nonetheless, I find myself not using that at all, since in most cases the tiled view allows for optimum use of screen real-estate in my opinion. If I can't see the entirety of a window it's kind of useless to me, so i'd prefer it be on a different workspace. But of course, floating one window like your calculator while your browser and RSS feed reader are tiled on the desktop is entirely possible and probably quite common. I do, however, use a popup rofi window with a custom script as a calculator, so that does indeed float near the top of my screen.