Happy New Year all. During my Christmas break, I performed a clean MacOS reinstallation and, in doing so, have lost the snowflake / magic configuration that allowed me to send meta to Emacs from my external WASD ISO USB keyboard. My keyboard has Mac printed keys and as typical on MacOS Alt to the left of cmd. However, I have to switch these in System Preferences so they work correctly. This works fine in all applications except Emacs where for example Alt-X which should translate as M-X ends up simply entering ≈ into the current buffer. I've tested all the typically problematic key mapping issues such as #, ", @ etc and all work fine in all apps + Emacs. It's purely this Alt / Meta issue. Pertinent emacs configuration:

(setq mac-option-key-is-meta t)
(setq mac-right-option-modifier nil)