I recently ran a little experiment to bring macOS's long-press-accents-like behavior to Emacs. What I forgot to mention is that macOS's character viewer just works from our beloved editor.
If you have a newer MacBook model, you can press the 🌐 key to summon the emoji picker (character viewer). You may need to set this key binding from macOS keyboard preferences.
I'm happy to take this Emacs freebie, kthxbye.
Edits:
(setq mac-command-modifier 'meta)
in your config.