Disable all system fn+letter keyboard shortcuts

I have the fn key set up as the Meta key for Emacs. But recently Mac OS (both 12.0.1 and 12.1) has started gobbling one or two combinations of fn plus a letter key: most notably, fn+N opens Notification Centre, even though I have no shortcut set up for ‘Show Notification Centre’ in System Preferences → Keyboard → Shortcuts → Mission Control. Since a lot of Emacs modes use M-n to mean ‘next’, this makes those shortcuts in Emacs unusable. I never use the systemwide fn-shortcuts. How do I defang them completely?