Thanks @jesus2099! I was about to create a customisation setting to select the key assigned to the menu, but ran in a problem where when changed and not working, there was no way out to change the key again because the setting option would have been in the menu itself.
@Lotheric in Opera then you just have to click out the input box to get the normal Ctrl+M working again. Sorry about that, but given the behavior, it’s not worth changing the script. I’ll add a note on Github about it, so everyone will know.