loukasgr As per documentation excerpt for screenshot added by you, Please understand in demo site too, the custom JS function is extended to one of parent menu item of mega menu and not JA ACM module
Create "More" menu item that show Off-canvas sidebar
In demo site, when you click on "More" menu item, it will show Off-canvas sidebar, this is custom function.
To be more precise and avoid confusion/ambiguity in addressing your query, Kindly provide clear visisble screenshot marked with annotations showing as to what relative issue is being faced in order to try to assist with the same