Desiree,
Have you tried this widget: https://appstore.home.mendix.com/link/app/111677/ to trigger a Select All button on the grid with keystrokes?
Mike
The only shortcut keys that Mendix uses are part of StudioPro, during editing, but not for during usage of the application.
You can create the shortcut by for yourself by adding a class to a datagrid’s SelectAll-button
and adding a javascript to the page that adds a function to every DOM-object having that class. What you need that javascript to do to select all lines of the datagrid … I don’t know.