I think that's just incorrect. There are varying conventions for spaces vs no spaces around em dashes, but all English manuals of style confine to en dashes just to things like "0–10" and "Louisville–Calgary" — at least to my knowledge.
> 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.
Remember I'm specifically speaking about british english.
But I see what you mean. There used to be a distinction between a shorter dash that is used for numerical ranges, or for things named after multiple people, and a longer dash used to connect independent clauses in a sentence [1]. I am shocked to hear that this distinction is being eroded.
[0] https://design.tax.service.gov.uk/hmrc-content-style-guide/
> Spaced en rules (or ‘en dashes’) must be used for parenthetical dashes. Hyphens or em rules (‘em dashes’) will not be accepted for either UK or US style books. En rules (–) are longer than hyphens (-) but shorter than em rules (—).
Section 2.1, "Editorial services style guide for academic books" https://www.cambridge.org/authorhub/resources/publishing-gui...