I always have been using em-dashes with specific spacing:
1. replacing parentheses —given that the em-dash in pairs for me mark more-relevant-to-the-main content than a parenthesized expression would— so I use the same spacing as `()`
2. replacing colon or just finishing the sentence with a subsentence— so the spacing goes like for a colon.
Probably unfounded grammatically and against any style guides, but this spacing makes sense to me.
I have never — not once — seen an LLM use it in pairs.