Hi @aldo.ercolani,
Here’s a tweaked version with the burger menus floating right and left correctly:
https://anvil.works/build#clone:U4OKNLRYGTBEEOQY=Y3JEWNHOW2IWJ3LOLKFUB7R7
All I did was to move your right-sidebar-toggle higher up in the HTML. Both the app-bar-nav and sidebar-toggle-right elements have the float: right; property. We need to apply the float: right; property to the sidebar before the app-bar-nav for it to remain the rightmost element.