Q:

Set Options Menu Visibility always On. (Android, Xamarin, MVVMCross)

I was wondering if there is a way to keep the Android options Menu programmatically permanently visible. 

A:

If I try to understand your question, it is a strange thing to do. If you want a menu to be visible all the time, then it has nothing to do with the options menu. Just create a (sub)view/layout with the menuitems you want to use.
Also remember the options menu can work differently between Android versions, and even certain  device vendors do funny things with the options menu, that could influence the way your app behaves.

