Using the New Outlook for Mac features in educational settings
Ok, so this isn't a general solution. For that, Microsoft will need to add an option to disable Option from triggering the menu navigation hints.
However, if you're desperate and/or you already use Keyboard Maestro, as discussed in the forum, the following macro works well for me. Just adjust the ⌥C and ⌘C commands to whatever Option-based shortcut you've been typing.