After you install ArcMenu, right click on it then click on ArcMenu settings.
From the settings page->"Menu Layout" in the sidebar->"Modern Layouts"->select "Eleven"->click Apply.
This will set the Windows 11 start menu layout as your app menu.
Now, if you want the menu to be centre aligned...
Click on "Customize Menu"->Change "Override Menu Location" toggle to "Bottom Centred"->click apply
Done! 
I like your wallpaper by the way...