I’ve built a custom layout for that (and a bunch of other symbols I frequently use). ⌥ hyphen for en-dash, ⌥ ⇧ hyphen for em-dash (and ⌥ M is for minus): https://typo.ale.sh/

(The idea isn’t new, of course: the default macOS layout’s 3rd layer is absolutely bonkers. I think Ilya Birman was the first: https://ilyabirman.net/typography-layout/)

those are the default macos keybindings for en-dash and em-dash characters

Good point, totally forgot about that :/