Hi Ólafur Klein,
Thanks for posting in the community, according to the decryption, I’ve tested on my side on Mac and Windows, I got the same result.
Based on this document, it is a built-in shortcut and it's not in the list of customizable keyboard shortcuts: Keyboard shortcuts in Word
If you want to type ”/” in Outline View, you can press the “/” key on the main keyboard, generally, it is on the left of the right-SHIFT key.
Besides, you can post an idea in UserVoice, it is best way to let the related team hear your needs, anyone’s suggestion could have a chance to be adopted by Microsoft.
Sorry for this inconvenience to your work, I hope the above information can help you a little.
Best Regards,
Arck