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There are conflicting systems in macOS at play here as a result of choosing the "Option" key as your "Meta" key. The basics of the Cocoa Emacs Keybindings (DefaultKeyBinding.dict) do allow for M-f/M-b/M-d to work as us Emacs users expect, however there is a conflict with the default US Keyboard Layout, which hijack these useful Option key sequences to allow for the easy input of letters with various diacritic markings. If you want to undo this, you can use a Keyboard Layout Editor like Ukelele[0] to make a custom layout that allows these key sequences to arrive unmolested at the Cocoa input system.

[0]: https://software.sil.org/ukelele/

Lol. Geez, we gotta do something about key sequences getting 'molested'...

I think that’s because the Meta key is the Option key on Macs which conflicts with some traditional keyboard shortcuts for other things in the OS.

For M-b and M-f, the equivalents are M-<left> and M-<right>