Recently I’ve been writing a lot for the German side of my personal site. When typing in German I perfer to use the English QWERTY keyboard and just alt-u-u to type “ü”. The problem I was having was emacs would intercept this and execute the capitalize-word function 😞. After some digging into my configs, ~/.doom.d/config.el, I was able to unset M-u only problem is it still didn’t activate the mac system umlaut feature.

(global-unset-key (kbd "M-u"))

Finally after some more digging I found:

(setq ns-alternate-modifier 'none
      ns-right-alternate-modifier 'meta)

It works by un-assigning the left alt to meta, allowing the system keyboard feature to kick in.

source: https://emacs.stackexchange.com/questions/61019/umlauts-in-emacs-on-mac