I would like to add a button to the "selection bar".
that would be present in all applications - or, in other words, I would like to modify the default buttons of this bar.
I've searched for it, however, it seems to me that most solutions are about modifying the bar of a specific app. For example this question - but I am not sure if the question is about the general modification that I want to do and I don't want to change the context menu, but the "selection bar".
So, is it possible to modify this bar? If yes, could someone please provide links/examples for the same.