how to let a layout cover the whole screen?

Well, showMenu may use less resources and may be sufficient for navigation and selecting single values out of a short list - but as soon as configuration becomes more complex (and this already begins with the choice of a specific color) or has to offer "Ok" and "Cancel" or even "Preview" opportunities (rather than just a simple "Back"), the menu system becomes really cumbersome to operate. Thats why I started writing components which look familiar for "normal" users.

Test person is my wife which does not care at all about technical constraints and efforts, but just wants a system like the Bangle.js to be easily usable - and she currently likes using a Bangle.js 2 although she did not wear any wrist watch for many years