Those shortcuts come from the Menu toolbar by default.
If you've turned it off entirely, you can tell Opus to still use the hotkeys in it by going to Customize / Toolbars, selecting Menu on the left, and checking Always enable this toolbar's keys in Listers on the right.
If the Menu toolbar has been edited to remove most of the items on it, you would need to create standalone hotkeys for them, or restore the menu to how it was originally.