Or British English.

The Oxford style guide page 18 https://www.ox.ac.uk/public-affairs/style-guide

m-dash (—)

Do not use; use an n-dash instead.

n-dash (–)

Use in a pair in place of round brackets or commas, surrounded by spaces.

I feel a number of people online started using something like the "British style", as an ascii hyphen is closer to an n-dash than an m-dash in width. And then without spaces either side looks very squished.